diff --git a/config.template.yml b/config.template.yml
index 6ced3277a..cea0b6663 100644
--- a/config.template.yml
+++ b/config.template.yml
@@ -131,12 +131,15 @@
     # authz:
       # forward-auth:
         # implementation: 'ForwardAuth'
+        # headers: ~
         # authn_strategies: []
       # ext-authz:
         # implementation: 'ExtAuthz'
+        # headers: ~
         # authn_strategies: []
       # auth-request:
         # implementation: 'AuthRequest'
+        # headers: ~
         # authn_strategies: []
       # legacy:
         # implementation: 'Legacy'
diff --git a/docs/content/configuration/miscellaneous/server-endpoints-authz.md b/docs/content/configuration/miscellaneous/server-endpoints-authz.md
index a3b363221..908db9251 100644
--- a/docs/content/configuration/miscellaneous/server-endpoints-authz.md
+++ b/docs/content/configuration/miscellaneous/server-endpoints-authz.md
@@ -33,6 +33,15 @@ server:
     authz:
       forward-auth:
         implementation: 'ForwardAuth'
+        headers:
+          Remote-User:
+            user_attribute: 'username'
+          Remote-Groups:
+            user_attribute: 'groups'
+          Remote-Name:
+            user_attribute: 'display_name'
+          Remote-Email:
+            user_attribute: 'email'
         authn_strategies:
           - name: 'HeaderAuthorization'
             schemes:
@@ -41,6 +50,15 @@ server:
           - name: 'CookieSession'
       ext-authz:
         implementation: 'ExtAuthz'
+        headers:
+          Remote-User:
+            user_attribute: 'username'
+          Remote-Groups:
+            user_attribute: 'groups'
+          Remote-Name:
+            user_attribute: 'display_name'
+          Remote-Email:
+            user_attribute: 'email'
         authn_strategies:
           - name: 'HeaderAuthorization'
             schemes:
@@ -49,6 +67,15 @@ server:
           - name: 'CookieSession'
       auth-request:
         implementation: 'AuthRequest'
+        headers:
+          Remote-User:
+            user_attribute: 'username'
+          Remote-Groups:
+            user_attribute: 'groups'
+          Remote-Name:
+            user_attribute: 'display_name'
+          Remote-Email:
+            user_attribute: 'email'
         authn_strategies:
           - name: 'HeaderAuthorization'
             schemes:
@@ -80,6 +107,31 @@ The underlying implementation for the endpoint. Valid case-sensitive values are
 `AuthRequest`, and `Legacy`. Read more about the implementations in the
 [reference guide](../../reference/guides/proxy-authorization.md#implementations).
 
+### headers
+
+{{< confkey type="dictionary(object)" required="no" >}}
+
+The headers value contains a dictionary where the dictionary key is the header name and the dictionary value is an
+object which determines the header value.
+
+The header name must only contain valid header name characters, and must not be a standard or otherwise reserved header
+such as `Content-Type`, `Location`, `Set-Cookie`, `WWW-Authenticate`, or any of the `Access-Control-*`, `X-Forwarded-*`,
+and `X-Original-*` headers. As header names are case-insensitive the same header must not be configured more than once
+in differing cases.
+
+Configuring this option replaces the default headers entirely, so the `Remote-User`, `Remote-Groups`, `Remote-Name`, and
+`Remote-Email` headers must be included if they are still required.
+
+#### user_attribute
+
+{{< confkey type="string" required="yes" >}}
+
+The user attribute to derive the header value from. This attribute can be one available from the authentication backend
+or one determined via the [User Attribute Definitions](../definitions/user-attributes.md). Attribute names which are not
+known to Authelia, and attributes which are not mapped by the configured authentication backend, cause a startup error.
+
+Attributes which resolve to a list are joined with a comma.
+
 ### authn_strategies
 
 {{< confkey type="list" required="no" >}}
diff --git a/internal/authentication/types.go b/internal/authentication/types.go
index 13c6fa5c3..41366949d 100644
--- a/internal/authentication/types.go
+++ b/internal/authentication/types.go
@@ -29,6 +29,10 @@ type UserDetails struct {
 
 // Addresses returns the Emails []string as []mail.Address formatted with DisplayName as the Name attribute.
 func (d *UserDetails) Addresses() (addresses []mail.Address) {
+	if d == nil {
+		return nil
+	}
+
 	if len(d.Emails) == 0 {
 		return nil
 	}
@@ -47,21 +51,37 @@ func (d *UserDetails) Addresses() (addresses []mail.Address) {
 
 // GetUsername returns the username.
 func (d *UserDetails) GetUsername() (username string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.Username
 }
 
 // GetGroups returns the groups.
 func (d *UserDetails) GetGroups() (groups []string) {
+	if d == nil {
+		return nil
+	}
+
 	return d.Groups
 }
 
 // GetDisplayName returns the display name.
 func (d *UserDetails) GetDisplayName() (name string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.DisplayName
 }
 
 // GetEmails returns the emails.
 func (d *UserDetails) GetEmails() (emails []string) {
+	if d == nil {
+		return nil
+	}
+
 	return d.Emails
 }
 
@@ -87,58 +107,147 @@ type UserDetailsExtended struct {
 	*UserDetails
 }
 
+// Addresses returns the Emails []string as []mail.Address formatted with DisplayName as the Name attribute.
+func (d *UserDetailsExtended) Addresses() (addresses []mail.Address) {
+	if d == nil {
+		return nil
+	}
+
+	return d.UserDetails.Addresses()
+}
+
+// GetUsername returns the username.
+func (d *UserDetailsExtended) GetUsername() (username string) {
+	if d == nil {
+		return ""
+	}
+
+	return d.UserDetails.GetUsername()
+}
+
+// GetGroups returns the groups.
+func (d *UserDetailsExtended) GetGroups() (groups []string) {
+	if d == nil {
+		return nil
+	}
+
+	return d.UserDetails.GetGroups()
+}
+
+// GetDisplayName returns the display name.
+func (d *UserDetailsExtended) GetDisplayName() (name string) {
+	if d == nil {
+		return ""
+	}
+
+	return d.UserDetails.GetDisplayName()
+}
+
+// GetEmails returns the emails.
+func (d *UserDetailsExtended) GetEmails() (emails []string) {
+	if d == nil {
+		return nil
+	}
+
+	return d.UserDetails.GetEmails()
+}
+
 // GetGivenName returns the given name.
 func (d *UserDetailsExtended) GetGivenName() (given string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.GivenName
 }
 
 // GetFamilyName returns the family name.
 func (d *UserDetailsExtended) GetFamilyName() (family string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.FamilyName
 }
 
 // GetMiddleName returns the middle name.
 func (d *UserDetailsExtended) GetMiddleName() (middle string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.MiddleName
 }
 
 // GetNickname returns the nickname.
 func (d *UserDetailsExtended) GetNickname() (nickname string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.Nickname
 }
 
 // GetProfile returns the profile URL as a string.
 func (d *UserDetailsExtended) GetProfile() (profile string) {
+	if d == nil {
+		return ""
+	}
+
 	return stringURL(d.Profile)
 }
 
 // GetPicture returns the picture URL as a string.
 func (d *UserDetailsExtended) GetPicture() (picture string) {
+	if d == nil {
+		return ""
+	}
+
 	return stringURL(d.Picture)
 }
 
 // GetWebsite returns the website URL as a string.
 func (d *UserDetailsExtended) GetWebsite() (website string) {
+	if d == nil {
+		return ""
+	}
+
 	return stringURL(d.Website)
 }
 
 // GetGender returns the gender.
 func (d *UserDetailsExtended) GetGender() (gender string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.Gender
 }
 
 // GetBirthdate returns the birthdate.
 func (d *UserDetailsExtended) GetBirthdate() (birthdate string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.Birthdate
 }
 
 // GetZoneInfo returns the zone information.
 func (d *UserDetailsExtended) GetZoneInfo() (info string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.ZoneInfo
 }
 
 // GetLocale returns the locale as a string.
 func (d *UserDetailsExtended) GetLocale() (locale string) {
+	if d == nil {
+		return ""
+	}
+
 	if d.Locale == nil {
 		return ""
 	}
@@ -148,16 +257,28 @@ func (d *UserDetailsExtended) GetLocale() (locale string) {
 
 // GetPhoneNumber returns the phone number without the extension.
 func (d *UserDetailsExtended) GetPhoneNumber() (number string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.PhoneNumber
 }
 
 // GetPhoneExtension returns the phone extension.
 func (d *UserDetailsExtended) GetPhoneExtension() (extension string) {
+	if d == nil {
+		return ""
+	}
+
 	return d.PhoneExtension
 }
 
 // GetPhoneNumberRFC3966 returns the phone number and extension formatted as per RFC3966.
 func (d *UserDetailsExtended) GetPhoneNumberRFC3966() (number string) {
+	if d == nil {
+		return ""
+	}
+
 	if d.PhoneNumber == "" {
 		return ""
 	}
@@ -171,6 +292,10 @@ func (d *UserDetailsExtended) GetPhoneNumberRFC3966() (number string) {
 
 // GetStreetAddress returns the street address.
 func (d *UserDetailsExtended) GetStreetAddress() (address string) {
+	if d == nil {
+		return ""
+	}
+
 	if d.Address == nil {
 		return ""
 	}
@@ -180,6 +305,10 @@ func (d *UserDetailsExtended) GetStreetAddress() (address string) {
 
 // GetLocality returns the locality.
 func (d *UserDetailsExtended) GetLocality() (locality string) {
+	if d == nil {
+		return ""
+	}
+
 	if d.Address == nil {
 		return ""
 	}
@@ -189,6 +318,10 @@ func (d *UserDetailsExtended) GetLocality() (locality string) {
 
 // GetRegion returns the region.
 func (d *UserDetailsExtended) GetRegion() (region string) {
+	if d == nil {
+		return ""
+	}
+
 	if d.Address == nil {
 		return ""
 	}
@@ -198,6 +331,10 @@ func (d *UserDetailsExtended) GetRegion() (region string) {
 
 // GetPostalCode returns the postal code.
 func (d *UserDetailsExtended) GetPostalCode() (postcode string) {
+	if d == nil {
+		return ""
+	}
+
 	if d.Address == nil {
 		return ""
 	}
@@ -207,6 +344,10 @@ func (d *UserDetailsExtended) GetPostalCode() (postcode string) {
 
 // GetCountry returns the country.
 func (d *UserDetailsExtended) GetCountry() (country string) {
+	if d == nil {
+		return ""
+	}
+
 	if d.Address == nil {
 		return ""
 	}
@@ -216,6 +357,10 @@ func (d *UserDetailsExtended) GetCountry() (country string) {
 
 // GetExtra returns the extra attributes.
 func (d *UserDetailsExtended) GetExtra() (extra map[string]any) {
+	if d == nil {
+		return nil
+	}
+
 	return d.Extra
 }
 
diff --git a/internal/configuration/config.template.yml b/internal/configuration/config.template.yml
index 6ced3277a..cea0b6663 100644
--- a/internal/configuration/config.template.yml
+++ b/internal/configuration/config.template.yml
@@ -131,12 +131,15 @@
     # authz:
       # forward-auth:
         # implementation: 'ForwardAuth'
+        # headers: ~
         # authn_strategies: []
       # ext-authz:
         # implementation: 'ExtAuthz'
+        # headers: ~
         # authn_strategies: []
       # auth-request:
         # implementation: 'AuthRequest'
+        # headers: ~
         # authn_strategies: []
       # legacy:
         # implementation: 'Legacy'
diff --git a/internal/configuration/schema/const.go b/internal/configuration/schema/const.go
index 8f34ded40..cf4e6c519 100644
--- a/internal/configuration/schema/const.go
+++ b/internal/configuration/schema/const.go
@@ -84,6 +84,20 @@ const (
 	RefreshIntervalDefault = time.Minute * 5
 )
 
+const (
+	// HeaderRemoteUser is the header which by default communicates the username of the authenticated user.
+	HeaderRemoteUser = "Remote-User"
+
+	// HeaderRemoteGroups is the header which by default communicates the groups of the authenticated user.
+	HeaderRemoteGroups = "Remote-Groups"
+
+	// HeaderRemoteName is the header which by default communicates the display name of the authenticated user.
+	HeaderRemoteName = "Remote-Name"
+
+	// HeaderRemoteEmail is the header which by default communicates the email of the authenticated user.
+	HeaderRemoteEmail = "Remote-Email"
+)
+
 const (
 	// LDAPImplementationCustom is the string for the custom LDAP implementation.
 	LDAPImplementationCustom = "custom"
diff --git a/internal/configuration/schema/keys.go b/internal/configuration/schema/keys.go
index b7d87b963..ee04af027 100644
--- a/internal/configuration/schema/keys.go
+++ b/internal/configuration/schema/keys.go
@@ -343,6 +343,9 @@ var Keys = []string{
 	"server.endpoints.authz.*.authn_strategies[].name",
 	"server.endpoints.authz.*.authn_strategies[].scheme_basic_cache_lifespan",
 	"server.endpoints.authz.*.authn_strategies[].schemes",
+	"server.endpoints.authz.*.headers",
+	"server.endpoints.authz.*.headers.*",
+	"server.endpoints.authz.*.headers.*.user_attribute",
 	"server.endpoints.authz.*.implementation",
 	"server.endpoints.enable_expvars",
 	"server.endpoints.enable_pprof",
diff --git a/internal/configuration/schema/server.go b/internal/configuration/schema/server.go
index 338818211..fb1de7b31 100644
--- a/internal/configuration/schema/server.go
+++ b/internal/configuration/schema/server.go
@@ -49,9 +49,16 @@ type ServerEndpointHealth struct {
 type ServerEndpointsAuthz struct {
 	Implementation string `koanf:"implementation" yaml:"implementation,omitempty" toml:"implementation,omitempty" json:"implementation,omitempty" jsonschema:"enum=ForwardAuth,enum=AuthRequest,enum=ExtAuthz,enum=Legacy,title=Implementation" jsonschema_description:"The specific Authorization implementation to use for this endpoint."`
 
+	Headers map[string]ServerEndpointsAuthzHeader `koanf:"headers" yaml:"headers,omitempty" toml:"headers,omitempty" json:"headers,omitempty" jsonschema:"title=Headers" jsonschema_description:"The specific Authorization headers to use for this endpoint."`
+
 	AuthnStrategies []ServerEndpointsAuthzAuthnStrategy `koanf:"authn_strategies" yaml:"authn_strategies,omitempty" toml:"authn_strategies,omitempty" json:"authn_strategies,omitempty" jsonschema:"title=Authn Strategies" jsonschema_description:"The specific Authorization strategies to use for this endpoint."`
 }
 
+// ServerEndpointsAuthzHeader is the Authz endpoint response header configuration for the HTTP server.
+type ServerEndpointsAuthzHeader struct {
+	UserAttribute string `koanf:"user_attribute" yaml:"user_attribute,omitempty" toml:"user_attribute,omitempty" json:"user_attribute,omitempty" jsonschema:"required,title=User Attribute" jsonschema_description:"The user attribute to use for the header."`
+}
+
 // ServerEndpointsAuthzAuthnStrategy is the Authz endpoints configuration for the HTTP server.
 type ServerEndpointsAuthzAuthnStrategy struct {
 	Name                     string        `koanf:"name" yaml:"name,omitempty" toml:"name,omitempty" json:"name,omitempty" jsonschema:"enum=HeaderAuthorization,enum=HeaderProxyAuthorization,enum=HeaderAuthRequestProxyAuthorization,enum=HeaderLegacy,enum=CookieSession,title=Name" jsonschema_description:"The name of the Authorization strategy to use."`
@@ -129,6 +136,20 @@ var DefaultServerConfiguration = Server{
 			},
 			AuthzEndpointNameAuthRequest: {
 				Implementation: AuthzImplementationAuthRequest,
+				Headers: map[string]ServerEndpointsAuthzHeader{
+					HeaderRemoteUser: {
+						UserAttribute: "username",
+					},
+					HeaderRemoteGroups: {
+						UserAttribute: "groups",
+					},
+					HeaderRemoteName: {
+						UserAttribute: "display_name",
+					},
+					HeaderRemoteEmail: {
+						UserAttribute: "email",
+					},
+				},
 				AuthnStrategies: []ServerEndpointsAuthzAuthnStrategy{
 					{
 						Name:    AuthzStrategyHeaderAuthorization,
@@ -141,6 +162,20 @@ var DefaultServerConfiguration = Server{
 			},
 			AuthzEndpointNameExtAuthz: {
 				Implementation: AuthzImplementationExtAuthz,
+				Headers: map[string]ServerEndpointsAuthzHeader{
+					HeaderRemoteUser: {
+						UserAttribute: "username",
+					},
+					HeaderRemoteGroups: {
+						UserAttribute: "groups",
+					},
+					HeaderRemoteName: {
+						UserAttribute: "display_name",
+					},
+					HeaderRemoteEmail: {
+						UserAttribute: "email",
+					},
+				},
 				AuthnStrategies: []ServerEndpointsAuthzAuthnStrategy{
 					{
 						Name:    AuthzStrategyHeaderAuthorization,
@@ -153,6 +188,20 @@ var DefaultServerConfiguration = Server{
 			},
 			AuthzEndpointNameForwardAuth: {
 				Implementation: AuthzImplementationForwardAuth,
+				Headers: map[string]ServerEndpointsAuthzHeader{
+					HeaderRemoteUser: {
+						UserAttribute: "username",
+					},
+					HeaderRemoteGroups: {
+						UserAttribute: "groups",
+					},
+					HeaderRemoteName: {
+						UserAttribute: "display_name",
+					},
+					HeaderRemoteEmail: {
+						UserAttribute: "email",
+					},
+				},
 				AuthnStrategies: []ServerEndpointsAuthzAuthnStrategy{
 					{
 						Name:    AuthzStrategyHeaderAuthorization,
diff --git a/internal/configuration/validator/const.go b/internal/configuration/validator/const.go
index 1fc5640a5..25a1556f2 100644
--- a/internal/configuration/validator/const.go
+++ b/internal/configuration/validator/const.go
@@ -445,22 +445,28 @@ const (
 	errFmtServerPathNotEndForwardSlash = "server: option 'address' must be a single subpath (i.e. '%s'), but '%s' contains multiple segments"
 	errFmtServerPathAlphaNumeric       = "server: option 'address' must have a path with only alphanumeric characters but it's configured as '%s'"
 
-	errFmtServerEndpointsAuthzImplementation            = "server: endpoints: authz: %s: option 'implementation' must be one of %s but it's configured as '%s'"
-	errFmtServerEndpointsAuthzStrategy                  = "server: endpoints: authz: %s: authn_strategies: option 'name' must be one of %s but it's configured as '%s'"
-	errFmtServerEndpointsAuthzSchemes                   = "server: endpoints: authz: %s: authn_strategies: strategy #%d (%s): option 'schemes' must only include the values %s but has '%s'"
-	errFmtServerEndpointsAuthzSchemesInvalidForStrategy = "server: endpoints: authz: %s: authn_strategies: strategy #%d (%s): option 'schemes' is not valid for the strategy"
-	errFmtServerEndpointsAuthzStrategyNoName            = "server: endpoints: authz: %s: authn_strategies: strategy #%d: option 'name' must be configured"
-	errFmtServerEndpointsAuthzStrategySchemeOnlyOption  = "server: endpoints: authz: %s: authn_strategies: strategy #%d: option '%s' can't be configured unless the '%s' scheme is configured but only the %s schemes are configured"
-	errFmtServerEndpointsAuthzStrategyDuplicate         = "server: endpoints: authz: %s: authn_strategies: duplicate strategy name detected with name '%s'"
-	errFmtServerEndpointsAuthzPrefixDuplicate           = "server: endpoints: authz: %s: endpoint starts with the same prefix as the '%s' endpoint with the '%s' implementation which accepts prefixes as part of its implementation"
-	errFmtServerEndpointsHealthProviderUnknown          = "server: endpoints: health: option 'providers' must only include the values %s but it's configured as '%s'"
-	errFmtServerEndpointsHealthProviderDuplicate        = "server: endpoints: health: option 'providers' has a duplicate value '%s'"
-	errFmtServerEndpointsHealthCacheNegative            = "server: endpoints: health: option 'cache' must be greater than or equal to 0 but it's configured as '%s'"
-	errFmtServerEndpointsHealthDetailedNotVerbose       = "server: endpoints: health: option 'detailed' has no effect unless option 'verbose' is enabled"
-	errFmtServerEndpointsRateLimitsBucketPeriodZero     = "server: endpoints: rate_limits: %s: bucket %d: option 'period' must have a value"
-	errFmtServerEndpointsRateLimitsBucketPeriodTooLow   = "server: endpoints: rate_limits: %s: bucket %d: option 'period' has a value of '%s' but it must be greater than 10 seconds"
-	errFmtServerEndpointsRateLimitsBucketRequestsZero   = "server: endpoints: rate_limits: %s: bucket %d: option 'requests' has a value of '%d' but it must be greater than 1"
-	errFmtServerEndpointsAuthzInvalidName               = "server: endpoints: authz: %s: contains invalid characters"
+	errFmtServerEndpointsAuthzOptionLegacy               = "server: endpoints: authz: %s: option '%s' must not be configured for the 'Legacy' implementation"
+	errFmtServerEndpointsAuthzHeaderInvalidName          = "server: endpoints: authz: %s: headers: %s: header name must only contain valid header name characters"
+	errFmtServerEndpointsAuthzHeaderReservedName         = "server: endpoints: authz: %s: headers: %s: header name must not be a standard or reserved header"
+	errFmtServerEndpointsAuthzHeaderDuplicateName        = "server: endpoints: authz: %s: headers: %s: header name duplicates the '%s' header as header names are case-insensitive"
+	errFmtServerEndpointsAuthzHeaderUserAttributeMissing = "server: endpoints: authz: %s: headers: %s: option 'user_attribute' is required"
+	errFmtServerEndpointsAuthzHeaderUserAttribute        = "server: endpoints: authz: %s: headers: %s: option 'user_attribute' must be a known user attribute but it's configured as '%s'"
+	errFmtServerEndpointsAuthzImplementation             = "server: endpoints: authz: %s: option 'implementation' must be one of %s but it's configured as '%s'"
+	errFmtServerEndpointsAuthzStrategy                   = "server: endpoints: authz: %s: authn_strategies: option 'name' must be one of %s but it's configured as '%s'"
+	errFmtServerEndpointsAuthzSchemes                    = "server: endpoints: authz: %s: authn_strategies: strategy #%d (%s): option 'schemes' must only include the values %s but has '%s'"
+	errFmtServerEndpointsAuthzSchemesInvalidForStrategy  = "server: endpoints: authz: %s: authn_strategies: strategy #%d (%s): option 'schemes' is not valid for the strategy"
+	errFmtServerEndpointsAuthzStrategyNoName             = "server: endpoints: authz: %s: authn_strategies: strategy #%d: option 'name' must be configured"
+	errFmtServerEndpointsAuthzStrategySchemeOnlyOption   = "server: endpoints: authz: %s: authn_strategies: strategy #%d: option '%s' can't be configured unless the '%s' scheme is configured but only the %s schemes are configured"
+	errFmtServerEndpointsAuthzStrategyDuplicate          = "server: endpoints: authz: %s: authn_strategies: duplicate strategy name detected with name '%s'"
+	errFmtServerEndpointsAuthzPrefixDuplicate            = "server: endpoints: authz: %s: endpoint starts with the same prefix as the '%s' endpoint with the '%s' implementation which accepts prefixes as part of its implementation"
+	errFmtServerEndpointsHealthProviderUnknown           = "server: endpoints: health: option 'providers' must only include the values %s but it's configured as '%s'"
+	errFmtServerEndpointsHealthProviderDuplicate         = "server: endpoints: health: option 'providers' has a duplicate value '%s'"
+	errFmtServerEndpointsHealthCacheNegative             = "server: endpoints: health: option 'cache' must be greater than or equal to 0 but it's configured as '%s'"
+	errFmtServerEndpointsHealthDetailedNotVerbose        = "server: endpoints: health: option 'detailed' has no effect unless option 'verbose' is enabled"
+	errFmtServerEndpointsRateLimitsBucketPeriodZero      = "server: endpoints: rate_limits: %s: bucket %d: option 'period' must have a value"
+	errFmtServerEndpointsRateLimitsBucketPeriodTooLow    = "server: endpoints: rate_limits: %s: bucket %d: option 'period' has a value of '%s' but it must be greater than 10 seconds"
+	errFmtServerEndpointsRateLimitsBucketRequestsZero    = "server: endpoints: rate_limits: %s: bucket %d: option 'requests' has a value of '%d' but it must be greater than 1"
+	errFmtServerEndpointsAuthzInvalidName                = "server: endpoints: authz: %s: contains invalid characters"
 
 	errFmtServerEndpointsAuthzLegacyInvalidImplementation = "server: endpoints: authz: %s: option 'implementation' is invalid: the endpoint with the name 'legacy' must use the 'Legacy' implementation"
 )
@@ -643,15 +649,20 @@ var (
 )
 
 var (
-	reKeyReplacer       = regexp.MustCompile(`\[\d+]`)
-	reDomainCharacters  = regexp.MustCompile(`^[a-z0-9](?:[a-z0-9-]*[a-z0-9])?(?:\.[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)+$`)
-	reAuthzEndpointName = regexp.MustCompile(`^[a-zA-Z](([a-zA-Z0-9/._-]*)([a-zA-Z]))?$`)
-	reOpenIDConnectKID  = regexp.MustCompile(`^([a-zA-Z0-9](([a-zA-Z0-9._~-]*)([a-zA-Z0-9]))?)?$`)
-	reRFC3986Unreserved = regexp.MustCompile(`^[a-zA-Z0-9._~-]+$`)
+	reKeyReplacer             = regexp.MustCompile(`\[\d+]`)
+	reDomainCharacters        = regexp.MustCompile(`^[a-z0-9](?:[a-z0-9-]*[a-z0-9])?(?:\.[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)+$`)
+	reAuthzEndpointName       = regexp.MustCompile(`^[a-zA-Z](([a-zA-Z0-9/._-]*)([a-zA-Z]))?$`)
+	reAuthzEndpointHeaderName = regexp.MustCompile("^[!#$%&'*+\\-.^_`|~0-9A-Za-z]+$")
+	reOpenIDConnectKID        = regexp.MustCompile(`^([a-zA-Z0-9](([a-zA-Z0-9._~-]*)([a-zA-Z0-9]))?)?$`)
+	reRFC3986Unreserved       = regexp.MustCompile(`^[a-zA-Z0-9._~-]+$`)
 )
 
 const (
 	attributeUserUsername       = "username"
+	attributeUserEmailVerified  = "email_verified"
+	attributeUserEmailsExtra    = "emails_extra"
+	attributeUserUpdatedAt      = "updated_at"
+	attributeUserAddress        = "address"
 	attributeUserGroups         = "groups"
 	attributeUserDisplayName    = "display_name"
 	attributeUserEmail          = "email"
@@ -669,13 +680,47 @@ const (
 	attributeUserLocale         = "locale"
 	attributeUserPhoneNumber    = "phone_number"
 	attributeUserPhoneExtension = "phone_extension"
-	attributeUserStreetAddress  = "street_address"
-	attributeUserLocality       = "locality"
-	attributeUserRegion         = "region"
-	attributeUserPostalCode     = "postal_code"
-	attributeUserCountry        = "country"
+
+	attributeUserPhoneNumberRFC3966  = "phone_number_rfc3966"
+	attributeUserPhoneNumberVerified = "phone_number_verified"
+
+	attributeUserStreetAddress = "street_address"
+	attributeUserLocality      = "locality"
+	attributeUserRegion        = "region"
+	attributeUserPostalCode    = "postal_code"
+	attributeUserCountry       = "country"
 )
 
+var reservedAuthzEndpointHeaderNames = []string{
+	// Message framing, representation metadata, and hop-by-hop headers.
+	"connection", "content-disposition", "content-encoding", "content-language", "content-length",
+	"content-location", "content-md5", "content-range", "content-type", "date", "expect", "forwarded", "host",
+	"keep-alive", "max-forwards", "proxy-connection", "range", "referer", "server", "te", "trailer",
+	"transfer-encoding", "upgrade", "user-agent", "via", "warning",
+
+	// Authentication, authorization, and session headers.
+	"authorization", "cookie", "proxy-authenticate", "proxy-authorization", "session-username", "set-cookie",
+	"www-authenticate",
+
+	// Redirection, caching, and conditional headers.
+	"age", "cache-control", "etag", "expires", "last-modified", "location", "pragma", "refresh", "retry-after",
+	"vary",
+
+	// Security headers.
+	"alt-svc", "clear-site-data", "content-security-policy", "content-security-policy-report-only", "expect-ct",
+	"feature-policy", "nel", "origin", "origin-agent-cluster", "permissions-policy", "referrer-policy",
+	"report-to", "strict-transport-security", "timing-allow-origin", "x-content-type-options",
+	"x-dns-prefetch-control", "x-download-options", "x-frame-options", "x-permitted-cross-domain-policies",
+	"x-xss-protection",
+
+	// Headers utilized by Authelia and the proxies which integrate with it.
+	"x-authelia-url", "x-real-ip",
+}
+
+var reservedAuthzEndpointHeaderPrefixes = []string{
+	"access-control-", "if-", "sec-", "x-forwarded-", "x-original-",
+}
+
 var validUserAttributes = []string{
 	attributeUserUsername,
 	attributeUserGroups,
diff --git a/internal/configuration/validator/server.go b/internal/configuration/validator/server.go
index a4ab120f6..a0bde0052 100644
--- a/internal/configuration/validator/server.go
+++ b/internal/configuration/validator/server.go
@@ -389,8 +389,6 @@ func validateServerEndpointsAuthzEndpoint(config *schema.Configuration, name str
 			break
 		case "":
 			endpoint.Implementation = schema.AuthzImplementationLegacy
-
-			config.Server.Endpoints.Authz[name] = endpoint
 		default:
 			if !utils.IsStringInSlice(endpoint.Implementation, validAuthzImplementations) {
 				validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzImplementation, name, utils.StringJoinOr(validAuthzImplementations), endpoint.Implementation))
@@ -405,6 +403,104 @@ func validateServerEndpointsAuthzEndpoint(config *schema.Configuration, name str
 	if !reAuthzEndpointName.MatchString(name) {
 		validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzInvalidName, name))
 	}
+
+	// NOTE: With exclusion of the implementation set any options below this line.
+	if endpoint.Implementation == schema.AuthzImplementationLegacy && endpoint.Headers != nil {
+		validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzOptionLegacy, name, "headers"))
+	}
+
+	if endpoint.Headers == nil {
+		switch endpoint.Implementation {
+		case schema.AuthzImplementationLegacy:
+			break
+		case schema.AuthzImplementationAuthRequest:
+			endpoint.Headers = schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameAuthRequest].Headers
+		case schema.AuthzImplementationExtAuthz:
+			endpoint.Headers = schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameExtAuthz].Headers
+		case schema.AuthzImplementationForwardAuth:
+			endpoint.Headers = schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameForwardAuth].Headers
+		}
+	} else {
+		validateServerEndpointsAuthzEndpointHeaders(config, name, endpoint, validator)
+	}
+
+	config.Server.Endpoints.Authz[name] = endpoint
+}
+
+func validateServerEndpointsAuthzEndpointHeaders(config *schema.Configuration, name string, endpoint schema.ServerEndpointsAuthz, validator *schema.StructValidator) {
+	headers := make([]string, 0, len(endpoint.Headers))
+
+	for header := range endpoint.Headers {
+		headers = append(headers, header)
+	}
+
+	sort.Strings(headers)
+
+	seen := make(map[string]string, len(headers))
+
+	for _, header := range headers {
+		validateServerEndpointsAuthzEndpointHeaderName(name, header, seen, validator)
+
+		switch attribute := endpoint.Headers[header].UserAttribute; {
+		case attribute == "":
+			validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzHeaderUserAttributeMissing, name, header))
+		case !isUserAttributeValidAuthz(attribute, config):
+			validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzHeaderUserAttribute, name, header, attribute))
+		}
+	}
+}
+
+func validateServerEndpointsAuthzEndpointHeaderName(name, header string, seen map[string]string, validator *schema.StructValidator) {
+	if !reAuthzEndpointHeaderName.MatchString(header) {
+		validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzHeaderInvalidName, name, header))
+
+		return
+	}
+
+	key := strings.ToLower(header)
+
+	if first, ok := seen[key]; ok {
+		validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzHeaderDuplicateName, name, header, first))
+
+		return
+	}
+
+	seen[key] = header
+
+	if utils.IsStringInSlice(key, reservedAuthzEndpointHeaderNames) {
+		validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzHeaderReservedName, name, header))
+
+		return
+	}
+
+	for _, prefix := range reservedAuthzEndpointHeaderPrefixes {
+		if strings.HasPrefix(key, prefix) {
+			validator.Push(fmt.Errorf(errFmtServerEndpointsAuthzHeaderReservedName, name, header))
+
+			return
+		}
+	}
+}
+
+func isUserAttributeValidAuthz(name string, config *schema.Configuration) (valid bool) {
+	if _, ok := config.Definitions.UserAttributes[name]; ok {
+		return true
+	}
+
+	switch name {
+	case attributeUserEmailVerified, attributeUserEmailsExtra, attributeUserUpdatedAt:
+		return true
+	case attributeUserPhoneNumberRFC3966, attributeUserPhoneNumberVerified:
+		return isUserAttributeValid(attributeUserPhoneNumber, config)
+	case attributeUserAddress:
+		return isUserAttributeValid(attributeUserStreetAddress, config) ||
+			isUserAttributeValid(attributeUserLocality, config) ||
+			isUserAttributeValid(attributeUserRegion, config) ||
+			isUserAttributeValid(attributeUserPostalCode, config) ||
+			isUserAttributeValid(attributeUserCountry, config)
+	default:
+		return isUserAttributeValid(name, config)
+	}
 }
 
 //nolint:gocyclo
diff --git a/internal/configuration/validator/server_test.go b/internal/configuration/validator/server_test.go
index a44f213de..6c158db6a 100644
--- a/internal/configuration/validator/server_test.go
+++ b/internal/configuration/validator/server_test.go
@@ -744,6 +744,7 @@ func TestServerAuthzEndpointDefaults(t *testing.T) {
 			map[string]schema.ServerEndpointsAuthz{
 				"example": {
 					Implementation: "ForwardAuth",
+					Headers:        schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameForwardAuth].Headers,
 					AuthnStrategies: []schema.ServerEndpointsAuthzAuthnStrategy{
 						{
 							Name:    "HeaderAuthorization",
@@ -762,6 +763,7 @@ func TestServerAuthzEndpointDefaults(t *testing.T) {
 			map[string]schema.ServerEndpointsAuthz{
 				"example": {
 					Implementation: "ForwardAuth",
+					Headers:        schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameForwardAuth].Headers,
 					AuthnStrategies: []schema.ServerEndpointsAuthzAuthnStrategy{
 						{
 							Name:    "HeaderAuthorization",
@@ -1078,3 +1080,201 @@ func TestValidateServerEndpointsHealth(t *testing.T) {
 		})
 	}
 }
+
+func TestServerAuthzEndpointHeaders(t *testing.T) {
+	testCases := []struct {
+		name    string
+		setup   func(config *schema.Configuration)
+		headers map[string]schema.ServerEndpointsAuthzHeader
+		errs    []string
+	}{
+		{
+			name: "ShouldAllowDefaultAttributes",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				schema.HeaderRemoteUser:   {UserAttribute: "username"},
+				schema.HeaderRemoteGroups: {UserAttribute: "groups"},
+				schema.HeaderRemoteName:   {UserAttribute: "display_name"},
+				schema.HeaderRemoteEmail:  {UserAttribute: "email"},
+			},
+		},
+		{
+			name: "ShouldAllowDerivedAttributes",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-Emails-Extra":          {UserAttribute: "emails_extra"},
+				"Remote-Email-Verified":        {UserAttribute: "email_verified"},
+				"Remote-Updated-At":            {UserAttribute: "updated_at"},
+				"Remote-Address":               {UserAttribute: "address"},
+				"Remote-Phone-Number-RFC3966":  {UserAttribute: "phone_number_rfc3966"},
+				"Remote-Phone-Number-Verified": {UserAttribute: "phone_number_verified"},
+			},
+		},
+		{
+			name: "ShouldAllowExtraAttributeFromFileBackend",
+			setup: func(config *schema.Configuration) {
+				config.AuthenticationBackend.File.ExtraAttributes = map[string]schema.AuthenticationBackendExtraAttribute{
+					"employee_id": {ValueType: "integer"},
+				}
+			},
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-Employee-Id": {UserAttribute: "employee_id"},
+			},
+		},
+		{
+			name: "ShouldAllowDefinedUserAttribute",
+			setup: func(config *schema.Configuration) {
+				config.Definitions.UserAttributes = map[string]schema.UserAttribute{
+					"is_admin": {Expression: "'admins' in groups"},
+				}
+			},
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-Is-Admin": {UserAttribute: "is_admin"},
+			},
+		},
+		{
+			name: "ShouldErrorOnUnknownAttributes",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-Mail":  {UserAttribute: "mail"},
+				"Remote-Teams": {UserAttribute: "teams"},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: Remote-Mail: option 'user_attribute' must be a known user attribute but it's configured as 'mail'",
+				"server: endpoints: authz: example: headers: Remote-Teams: option 'user_attribute' must be a known user attribute but it's configured as 'teams'",
+			},
+		},
+		{
+			name: "ShouldErrorOnInvalidHeaderNames",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote User":  {UserAttribute: "username"},
+				"Remote:Group": {UserAttribute: "groups"},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: Remote User: header name must only contain valid header name characters",
+				"server: endpoints: authz: example: headers: Remote:Group: header name must only contain valid header name characters",
+			},
+		},
+		{
+			name: "ShouldErrorOnReservedHeaderNames",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Content-Type":     {UserAttribute: "username"},
+				"Location":         {UserAttribute: "username"},
+				"set-cookie":       {UserAttribute: "username"},
+				"WWW-Authenticate": {UserAttribute: "username"},
+				"X-Authelia-URL":   {UserAttribute: "username"},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: Content-Type: header name must not be a standard or reserved header",
+				"server: endpoints: authz: example: headers: Location: header name must not be a standard or reserved header",
+				"server: endpoints: authz: example: headers: WWW-Authenticate: header name must not be a standard or reserved header",
+				"server: endpoints: authz: example: headers: X-Authelia-URL: header name must not be a standard or reserved header",
+				"server: endpoints: authz: example: headers: set-cookie: header name must not be a standard or reserved header",
+			},
+		},
+		{
+			name: "ShouldErrorOnReservedHeaderNamePrefixes",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Access-Control-Allow-Origin": {UserAttribute: "username"},
+				"Sec-Fetch-Site":              {UserAttribute: "username"},
+				"X-Forwarded-User":            {UserAttribute: "username"},
+				"X-Original-User":             {UserAttribute: "username"},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: Access-Control-Allow-Origin: header name must not be a standard or reserved header",
+				"server: endpoints: authz: example: headers: Sec-Fetch-Site: header name must not be a standard or reserved header",
+				"server: endpoints: authz: example: headers: X-Forwarded-User: header name must not be a standard or reserved header",
+				"server: endpoints: authz: example: headers: X-Original-User: header name must not be a standard or reserved header",
+			},
+		},
+		{
+			name: "ShouldErrorOnDuplicateHeaderNames",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-User": {UserAttribute: "username"},
+				"remote-user": {UserAttribute: "display_name"},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: remote-user: header name duplicates the 'Remote-User' header as header names are case-insensitive",
+			},
+		},
+		{
+			name: "ShouldAllowUncommonButValidHeaderNames",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote_User":   {UserAttribute: "username"},
+				"X-Team+Name":   {UserAttribute: "display_name"},
+				"Remote-Groups": {UserAttribute: "groups"},
+			},
+		},
+		{
+			name: "ShouldErrorOnMissingUserAttribute",
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-User": {},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: Remote-User: option 'user_attribute' is required",
+			},
+		},
+		{
+			name: "ShouldErrorOnAttributeNotMappedByLDAPBackend",
+			setup: func(config *schema.Configuration) {
+				config.AuthenticationBackend.File = nil
+				config.AuthenticationBackend.LDAP = &schema.AuthenticationBackendLDAP{}
+			},
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-Given-Name": {UserAttribute: "given_name"},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: Remote-Given-Name: option 'user_attribute' must be a known user attribute but it's configured as 'given_name'",
+			},
+		},
+		{
+			name: "ShouldAllowAttributeMappedByLDAPBackend",
+			setup: func(config *schema.Configuration) {
+				config.AuthenticationBackend.File = nil
+				config.AuthenticationBackend.LDAP = &schema.AuthenticationBackendLDAP{}
+				config.AuthenticationBackend.LDAP.Attributes.GivenName = "givenName"
+				config.AuthenticationBackend.LDAP.Attributes.PhoneNumber = "telephoneNumber"
+			},
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-Given-Name":           {UserAttribute: "given_name"},
+				"Remote-Phone-Number-RFC3966": {UserAttribute: "phone_number_rfc3966"},
+				"Remote-Updated-At":           {UserAttribute: "updated_at"},
+			},
+		},
+		{
+			name: "ShouldErrorOnDerivedAddressNotMappedByLDAPBackend",
+			setup: func(config *schema.Configuration) {
+				config.AuthenticationBackend.File = nil
+				config.AuthenticationBackend.LDAP = &schema.AuthenticationBackendLDAP{}
+			},
+			headers: map[string]schema.ServerEndpointsAuthzHeader{
+				"Remote-Address": {UserAttribute: "address"},
+			},
+			errs: []string{
+				"server: endpoints: authz: example: headers: Remote-Address: option 'user_attribute' must be a known user attribute but it's configured as 'address'",
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			validator := schema.NewStructValidator()
+
+			config := newDefaultConfig()
+
+			if tc.setup != nil {
+				tc.setup(&config)
+			}
+
+			config.Server.Endpoints.Authz = map[string]schema.ServerEndpointsAuthz{
+				"example": {Implementation: schema.AuthzImplementationForwardAuth, Headers: tc.headers},
+			}
+
+			ValidateServerEndpoints(&config, validator)
+
+			assert.Len(t, validator.Warnings(), 0)
+			require.Len(t, validator.Errors(), len(tc.errs))
+
+			for i, expected := range tc.errs {
+				assert.EqualError(t, validator.Errors()[i], expected)
+			}
+		})
+	}
+}
diff --git a/internal/handlers/const.go b/internal/handlers/const.go
index dcd818631..005ca163d 100644
--- a/internal/handlers/const.go
+++ b/internal/handlers/const.go
@@ -9,6 +9,7 @@ import (
 
 	"github.com/valyala/fasthttp"
 
+	"github.com/authelia/authelia/v4/internal/configuration/schema"
 	"github.com/authelia/authelia/v4/internal/oidc"
 )
 
@@ -29,10 +30,10 @@ var (
 	headerProxyAuthenticate  = []byte(fasthttp.HeaderProxyAuthenticate)
 
 	headerSessionUsername = []byte("Session-Username")
-	headerRemoteUser      = []byte("Remote-User")
-	headerRemoteGroups    = []byte("Remote-Groups")
-	headerRemoteName      = []byte("Remote-Name")
-	headerRemoteEmail     = []byte("Remote-Email")
+	headerRemoteUser      = []byte(schema.HeaderRemoteUser)
+	headerRemoteGroups    = []byte(schema.HeaderRemoteGroups)
+	headerRemoteName      = []byte(schema.HeaderRemoteName)
+	headerRemoteEmail     = []byte(schema.HeaderRemoteEmail)
 )
 
 const (
diff --git a/internal/handlers/handler_authz.go b/internal/handlers/handler_authz.go
index 796de94d9..a5b549b98 100644
--- a/internal/handlers/handler_authz.go
+++ b/internal/handlers/handler_authz.go
@@ -206,8 +206,8 @@ func (authz *Authz) Handler(ctx AuthzContext) {
 
 	ruleHasSubject, required := ctx.GetProviders().Authorizer.GetRequiredLevel(
 		authorization.Subject{
-			Username: authn.Details.Username,
-			Groups:   authn.Details.Groups,
+			Username: authn.Details.GetUsername(),
+			Groups:   authn.Details.GetGroups(),
 			ClientID: authn.ClientID,
 			IP:       ctx.RemoteIP(),
 		},
@@ -251,7 +251,7 @@ func (authz *Authz) Handler(ctx AuthzContext) {
 
 		handler(ctx, authn, authz.getRedirectionURL(&object, autheliaURL))
 	case AuthzResultAuthorized:
-		authz.handleAuthorized(ctx, authn)
+		authz.handleAuthorized(ctx, authz.headers, authn)
 	}
 }
 
@@ -307,7 +307,7 @@ func (authz *Authz) authn(ctx AuthzContext, manager session.Manager, object *aut
 			authn.Level = authentication.NotAuthenticated
 			authn.Username = anonymous
 			authn.ClientID = ""
-			authn.Details = authentication.UserDetails{}
+			authn.Details = &authentication.UserDetailsExtended{UserDetails: &authentication.UserDetails{}}
 
 			if strategy.CanHandleUnauthorized() {
 				return authn, strategy, err
@@ -321,7 +321,7 @@ func (authz *Authz) authn(ctx AuthzContext, manager session.Manager, object *aut
 		}
 	}
 
-	if strategy.CanHandleUnauthorized() {
+	if strategy != nil && strategy.CanHandleUnauthorized() {
 		return authn, strategy, err
 	}
 
diff --git a/internal/handlers/handler_authz_authn.go b/internal/handlers/handler_authz_authn.go
index 256945ccd..9ae963f83 100644
--- a/internal/handlers/handler_authz_authn.go
+++ b/internal/handlers/handler_authz_authn.go
@@ -93,9 +93,13 @@ func NewHeaderLegacyAuthnStrategy() *HeaderLegacyAuthnStrategy {
 // CookieSessionAuthnStrategy is a session cookie AuthnStrategy.
 type CookieSessionAuthnStrategy struct {
 	refresh schema.RefreshIntervalDuration
+
+	extended bool
 }
 
 // Get returns the Authn information for this AuthnStrategy.
+//
+//nolint:gocyclo
 func (s *CookieSessionAuthnStrategy) Get(ctx AuthzContext, manager session.Manager, _ *authorization.Object) (authn *Authn, err error) {
 	var userSession session.UserSession
 
@@ -142,16 +146,47 @@ func (s *CookieSessionAuthnStrategy) Get(ctx AuthzContext, manager session.Manag
 		}
 	}
 
+	if !s.extended || userSession.Username == "" {
+		return &Authn{
+			Username: friendlyUsername(userSession.Username),
+			Details: &authentication.UserDetailsExtended{
+				UserDetails: &authentication.UserDetails{
+					Username:    userSession.Username,
+					DisplayName: userSession.DisplayName,
+					Emails:      userSession.Emails,
+					Groups:      userSession.Groups,
+				},
+			},
+			Level: userSession.AuthenticationLevel(ctx.GetConfiguration().WebAuthn.EnablePasskey2FA),
+			Type:  AuthnTypeCookie,
+		}, nil
+	}
+
+	var details *authentication.UserDetailsExtended
+
+	if details, err = ctx.GetUserProvider().GetDetailsExtended(userSession.Username); err != nil {
+		if errors.Is(err, authentication.ErrUserNotFound) {
+			ctx.GetLogger().WithField("username", userSession.Username).Error("Error occurred while attempting to get user details for user: the user was not found indicating they were deleted, disabled, or otherwise no longer authorized to login")
+
+			return authn, err
+		}
+
+		return authn, fmt.Errorf("unable to retrieve details for user '%s': %w", userSession.Username, err)
+	} else if details == nil || details.GetUsername() == "" {
+		ctx.GetLogger().WithField("username", userSession.Username).Error("Error occurred while attempting to get user details for user: no user details were returned")
+
+		if err = manager.DestroySession(); err != nil {
+			ctx.GetLogger().WithError(err).Errorf("Unable to destroy user session")
+		}
+
+		return authn, fmt.Errorf("unable to retrieve details for user '%s': no user details were returned", userSession.Username)
+	}
+
 	return &Authn{
 		Username: friendlyUsername(userSession.Username),
-		Details: authentication.UserDetails{
-			Username:    userSession.Username,
-			DisplayName: userSession.DisplayName,
-			Emails:      userSession.Emails,
-			Groups:      userSession.Groups,
-		},
-		Level: userSession.AuthenticationLevel(ctx.GetConfiguration().WebAuthn.EnablePasskey2FA),
-		Type:  AuthnTypeCookie,
+		Details:  details,
+		Level:    userSession.AuthenticationLevel(ctx.GetConfiguration().WebAuthn.EnablePasskey2FA),
+		Type:     AuthnTypeCookie,
 	}, nil
 }
 
@@ -180,6 +215,8 @@ type HeaderAuthnStrategy struct {
 
 	delay middlewares.Delayer
 	basic BasicAuthHandler
+
+	extended bool
 }
 
 // BasicAuthHandler is a function signature that handles basic authentication. This is used to implement caching. The
@@ -252,13 +289,13 @@ func (s *HeaderAuthnStrategy) Get(ctx AuthzContext, _ session.Manager, object *a
 		return authn, nil
 	}
 
-	var details *authentication.UserDetails
+	var details *authentication.UserDetailsExtended
 
 	switch scheme {
 	case model.AuthorizationSchemeBasic:
-		details, level, err = handleGetBasic(ctx, s.delay, authn, object, s.headerAuthorize, s.basic)
+		details, level, err = handleGetBasic(ctx, s.delay, authn, object, s.headerAuthorize, s.basic, s.extended)
 	case model.AuthorizationSchemeBearer:
-		details, clientID, ccs, level, err = handleVerifyGETAuthorizationBearer(ctx, authn, object)
+		details, clientID, ccs, level, err = handleVerifyGETAuthorizationBearer(ctx, authn, object, s.extended)
 	default:
 		ctx.GetLogger().
 			WithFields(map[string]any{"scheme": authn.Header.Authorization.SchemeRaw(), "header": string(s.headerAuthorize)}).
@@ -288,7 +325,7 @@ func (s *HeaderAuthnStrategy) Get(ctx AuthzContext, _ session.Manager, object *a
 		return authn, fmt.Errorf("failed to determine username from the %s header", s.headerAuthorize)
 	default:
 		authn.Username = friendlyUsername(details.Username)
-		authn.Details = *details
+		authn.Details = details
 	}
 
 	authn.Level = level
@@ -322,6 +359,8 @@ func (s *HeaderAuthnStrategy) HandleUnauthorized(ctx AuthzContext, authn *Authn,
 // HeaderLegacyAuthnStrategy is a legacy header AuthnStrategy which can be switched based on the query parameters.
 type HeaderLegacyAuthnStrategy struct {
 	delay middlewares.Delayer
+
+	extended bool
 }
 
 // Get returns the Authn information for this AuthnStrategy.
@@ -373,16 +412,16 @@ func (s *HeaderLegacyAuthnStrategy) Get(ctx AuthzContext, _ session.Manager, obj
 	}
 
 	var (
-		details *authentication.UserDetails
+		details *authentication.UserDetailsExtended
 		level   authentication.Level
 	)
 
-	if details, level, err = handleGetBasic(ctx, s.delay, authn, object, header, DefaultBasicAuthHandler); err != nil {
+	if details, level, err = handleGetBasic(ctx, s.delay, authn, object, header, DefaultBasicAuthHandler, s.extended); err != nil {
 		return authn, fmt.Errorf("failed to validate %s header with %s scheme: %w", header, scheme, err)
 	}
 
 	authn.Username = friendlyUsername(details.Username)
-	authn.Details = *details
+	authn.Details = details
 	authn.Level = level
 
 	return authn, nil
@@ -403,7 +442,7 @@ func (s *HeaderLegacyAuthnStrategy) HandleUnauthorized(ctx AuthzContext, authn *
 	handleAuthzUnauthorizedAuthorizationBasic(ctx, authn)
 }
 
-func handleGetBasic(ctx AuthzContext, delayer middlewares.Delayer, authn *Authn, object *authorization.Object, header []byte, validate BasicAuthHandler) (details *authentication.UserDetails, level authentication.Level, err error) {
+func handleGetBasic(ctx AuthzContext, delayer middlewares.Delayer, authn *Authn, object *authorization.Object, header []byte, validate BasicAuthHandler, extended bool) (details *authentication.UserDetailsExtended, level authentication.Level, err error) {
 	var (
 		ban           regulation.BanType
 		value         string
@@ -421,7 +460,7 @@ func handleGetBasic(ctx AuthzContext, delayer middlewares.Delayer, authn *Authn,
 		return nil, authentication.NotAuthenticated, fmt.Errorf("failed to validate parsed credentials of %s header: the username or password was empty", header)
 	}
 
-	if details, err = ctx.GetUserProvider().GetDetails(username); err != nil {
+	if details, err = handleGetUserDetails(ctx, username, extended); err != nil {
 		if errors.Is(err, authentication.ErrUserNotFound) {
 			doMarkAuthenticationAttemptWithRequest(ctx, false, regulation.NewBan(regulation.BanTypeUnknown, "", nil), regulation.AuthType1FA, object.String(), object.Method, err)
 
@@ -472,9 +511,27 @@ func handleGetBasic(ctx AuthzContext, delayer middlewares.Delayer, authn *Authn,
 	return details, authentication.OneFactor, nil
 }
 
+func handleGetUserDetails(ctx AuthzContext, username string, extended bool) (details *authentication.UserDetailsExtended, err error) {
+	if extended {
+		return ctx.GetUserProvider().GetDetailsExtended(username)
+	}
+
+	var basic *authentication.UserDetails
+
+	if basic, err = ctx.GetUserProvider().GetDetails(username); err != nil {
+		return nil, err
+	}
+
+	if basic == nil {
+		return nil, nil
+	}
+
+	return &authentication.UserDetailsExtended{UserDetails: basic}, nil
+}
+
 func handleAuthnCookieValidate(ctx AuthzContext, manager session.Manager, userSession *session.UserSession, refresh schema.RefreshIntervalDuration) (modified, invalid bool) {
 	// TODO: Remove this check as it's no longer possible i.e. ineffectual.
-	isAnonymous := userSession.Username == ""
+	isAnonymous := userSession.IsAnonymous()
 
 	if isAnonymous && userSession.AuthenticationLevel(ctx.GetConfiguration().WebAuthn.EnablePasskey2FA) != authentication.NotAuthenticated {
 		ctx.GetLogger().WithFields(map[string]any{"username": anonymous, "level": userSession.AuthenticationLevel(ctx.GetConfiguration().WebAuthn.EnablePasskey2FA).String()}).Errorf("Session for user has an invalid authentication level: this may be a sign of a compromise")
@@ -578,7 +635,7 @@ func handleSessionValidateRefresh(ctx AuthzContext, userSession *session.UserSes
 	return true, false
 }
 
-func handleVerifyGETAuthorizationBearer(ctx AuthzContext, authn *Authn, object *authorization.Object) (details *authentication.UserDetails, clientID string, ccs bool, level authentication.Level, err error) {
+func handleVerifyGETAuthorizationBearer(ctx AuthzContext, authn *Authn, object *authorization.Object, extended bool) (details *authentication.UserDetailsExtended, clientID string, ccs bool, level authentication.Level, err error) {
 	var at bool
 
 	if at, err = oidc.IsAccessToken(ctx, authn.Header.Authorization.Value()); !at {
@@ -597,15 +654,15 @@ func handleVerifyGETAuthorizationBearer(ctx AuthzContext, authn *Authn, object *
 		return nil, "", false, authentication.NotAuthenticated, err
 	}
 
-	return handleVerifyGETAuthorizationBearerResolveUser(ctx, username, clientID, ccs, level)
+	return handleVerifyGETAuthorizationBearerResolveUser(ctx, username, clientID, ccs, level, extended)
 }
 
-func handleVerifyGETAuthorizationBearerResolveUser(ctx AuthzContext, username, clientID string, ccs bool, level authentication.Level) (details *authentication.UserDetails, clientIDOut string, ccsOut bool, levelOut authentication.Level, err error) {
+func handleVerifyGETAuthorizationBearerResolveUser(ctx AuthzContext, username, clientID string, ccs bool, level authentication.Level, extended bool) (details *authentication.UserDetailsExtended, clientIDOut string, ccsOut bool, levelOut authentication.Level, err error) {
 	if ccs {
 		return nil, clientID, ccs, level, nil
 	}
 
-	if details, err = ctx.GetUserProvider().GetDetails(username); err != nil {
+	if details, err = handleGetUserDetails(ctx, username, extended); err != nil {
 		if errors.Is(err, authentication.ErrUserNotFound) {
 			ctx.GetLogger().WithField("username", username).Error("Error occurred while attempting to get user details for user: the user was not found indicating they were deleted, disabled, or otherwise no longer authorized to login")
 		}
diff --git a/internal/handlers/handler_authz_builder.go b/internal/handlers/handler_authz_builder.go
index 1a9abc974..5394f18c1 100644
--- a/internal/handlers/handler_authz_builder.go
+++ b/internal/handlers/handler_authz_builder.go
@@ -73,9 +73,18 @@ func (b *AuthzBuilder) WithConfig(config *schema.Configuration) *AuthzBuilder {
 	return b
 }
 
+// WithEndpointHeaders configures the AuthzBuilder with the response headers for this endpoint.
+func (b *AuthzBuilder) WithEndpointHeaders(headers map[string]schema.ServerEndpointsAuthzHeader) *AuthzBuilder {
+	b.headers = headers
+
+	return b
+}
+
 // WithEndpointConfig configures the AuthzBuilder with a *schema.ServerAuthzEndpointConfig. Should be called AFTER
 // WithConfig or WithAuthzConfig.
 func (b *AuthzBuilder) WithEndpointConfig(config schema.ServerEndpointsAuthz) *AuthzBuilder {
+	b.WithEndpointHeaders(config.Headers)
+
 	switch config.Implementation {
 	case AuthzImplForwardAuth.String():
 		b.WithImplementationForwardAuth()
@@ -129,9 +138,27 @@ func (b *AuthzBuilder) Build() (authz *Authz) {
 		}
 	}
 
+	for header, config := range b.headers {
+		authz.headers = append(authz.headers, AuthzHeader{Key: []byte(header), Attribute: config.UserAttribute})
+	}
+
+	extended := authzHeadersRequireExtendedUserDetails(authz.headers)
+
+	for _, v := range authz.strategies {
+		switch strategy := v.(type) {
+		case *CookieSessionAuthnStrategy:
+			strategy.extended = extended
+		case *HeaderAuthnStrategy:
+			strategy.extended = extended
+		case *HeaderLegacyAuthnStrategy:
+			strategy.extended = extended
+		}
+	}
+
 	switch b.implementation {
 	case AuthzImplLegacy:
 		authz.config.StatusCodeBadRequest = fasthttp.StatusUnauthorized
+		authz.handleAuthorized = handleAuthzAuthorizedLegacy
 		authz.handleGetObject = handleAuthzGetObjectLegacy
 		authz.handleUnauthorized = handleAuthzUnauthorizedLegacy
 		authz.handleGetAutheliaURL = handleAuthzPortalURLLegacy
diff --git a/internal/handlers/handler_authz_common.go b/internal/handlers/handler_authz_common.go
index ba41538b3..bf8354726 100644
--- a/internal/handlers/handler_authz_common.go
+++ b/internal/handlers/handler_authz_common.go
@@ -35,19 +35,40 @@ func handleAuthzPortalURLFromQueryLegacy(ctx AuthzContext) (portalURL *url.URL,
 	return parseAuthzPortalURL(ctx.GetRequestQueryArgValue(qryArgRD))
 }
 
-func handleAuthzAuthorizedStandard(ctx AuthzContext, authn *Authn) {
+func handleAuthzAuthorizedStandard(ctx AuthzContext, headers []AuthzHeader, authn *Authn) {
 	ctx.ReplyStatusCode(fasthttp.StatusOK)
 
-	if authn.Details.Username != "" {
-		ctx.SetResponseHeaderValue(headerRemoteUser, authn.Details.Username)
-		ctx.SetResponseHeaderValue(headerRemoteGroups, strings.Join(authn.Details.Groups, ","))
-		ctx.SetResponseHeaderValue(headerRemoteName, authn.Details.DisplayName)
+	if authn.Details.GetUsername() == "" {
+		return
+	}
 
-		switch len(authn.Details.Emails) {
+	resolver, updated := ctx.GetProviderUserAttributeResolver(), ctx.GetClock().Now()
+
+	for _, header := range headers {
+		object, ok := resolver.Resolve(header.Attribute, authn.Details, updated)
+		if !ok {
+			ctx.SetResponseHeaderValue(header.Key, "")
+
+			continue
+		}
+
+		ctx.SetResponseHeaderValue(header.Key, authzHeaderValue(object))
+	}
+}
+
+func handleAuthzAuthorizedLegacy(ctx AuthzContext, _ []AuthzHeader, authn *Authn) {
+	ctx.ReplyStatusCode(fasthttp.StatusOK)
+
+	if authn.Details.GetUsername() != "" {
+		ctx.SetResponseHeaderValue(headerRemoteUser, authn.Details.GetUsername())
+		ctx.SetResponseHeaderValue(headerRemoteGroups, strings.Join(authn.Details.GetGroups(), ","))
+		ctx.SetResponseHeaderValue(headerRemoteName, authn.Details.GetDisplayName())
+
+		switch emails := authn.Details.GetEmails(); len(emails) {
 		case 0:
 			ctx.SetResponseHeaderValue(headerRemoteEmail, "")
 		default:
-			ctx.SetResponseHeaderValue(headerRemoteEmail, authn.Details.Emails[0])
+			ctx.SetResponseHeaderValue(headerRemoteEmail, emails[0])
 		}
 	}
 }
diff --git a/internal/handlers/handler_authz_misc_test.go b/internal/handlers/handler_authz_misc_test.go
index 60fe3583d..a763fc0b0 100644
--- a/internal/handlers/handler_authz_misc_test.go
+++ b/internal/handlers/handler_authz_misc_test.go
@@ -93,7 +93,7 @@ func TestHandleGetBasicShouldRejectEmptyCredentialsWithDelay(t *testing.T) {
 
 			object := authorization.NewObject(targetURL, fasthttp.MethodGet)
 
-			details, level, err := handleGetBasic(mock.Ctx, delayer, authn, &object, headerProxyAuthorization, DefaultBasicAuthHandler)
+			details, level, err := handleGetBasic(mock.Ctx, delayer, authn, &object, headerProxyAuthorization, DefaultBasicAuthHandler, false)
 
 			require.EqualError(t, err, tc.ExpectError)
 			assert.Nil(t, details)
@@ -120,8 +120,9 @@ func TestHandleVerifyGETAuthorizationBearerResolveUser(t *testing.T) {
 		ClientID      string
 		CCS           bool
 		Level         authentication.Level
+		Extended      bool
 		Setup         func(mock *mocks.MockAutheliaCtx)
-		ExpectDetails *authentication.UserDetails
+		ExpectDetails *authentication.UserDetailsExtended
 		ExpectError   string
 	}{
 		{
@@ -132,6 +133,7 @@ func TestHandleVerifyGETAuthorizationBearerResolveUser(t *testing.T) {
 			Level:    authentication.OneFactor,
 			Setup: func(mock *mocks.MockAutheliaCtx) {
 				mock.UserProviderMock.EXPECT().GetDetails(gomock.Any()).Times(0)
+				mock.UserProviderMock.EXPECT().GetDetailsExtended(gomock.Any()).Times(0)
 			},
 			ExpectDetails: nil,
 		},
@@ -142,11 +144,27 @@ func TestHandleVerifyGETAuthorizationBearerResolveUser(t *testing.T) {
 			CCS:      false,
 			Level:    authentication.OneFactor,
 			Setup: func(mock *mocks.MockAutheliaCtx) {
+				mock.UserProviderMock.EXPECT().GetDetailsExtended(gomock.Any()).Times(0)
 				mock.UserProviderMock.EXPECT().
 					GetDetails(gomock.Eq("john")).
 					Return(&authentication.UserDetails{Username: "john"}, nil)
 			},
-			ExpectDetails: &authentication.UserDetails{Username: "john"},
+			ExpectDetails: &authentication.UserDetailsExtended{UserDetails: &authentication.UserDetails{Username: "john"}},
+		},
+		{
+			Name:     "ShouldResolveExtendedDetailsForUserBoundTokenWhenHeadersRequireThem",
+			Username: "john",
+			ClientID: "",
+			CCS:      false,
+			Level:    authentication.OneFactor,
+			Extended: true,
+			Setup: func(mock *mocks.MockAutheliaCtx) {
+				mock.UserProviderMock.EXPECT().GetDetails(gomock.Any()).Times(0)
+				mock.UserProviderMock.EXPECT().
+					GetDetailsExtended(gomock.Eq("john")).
+					Return(&authentication.UserDetailsExtended{GivenName: "John", UserDetails: &authentication.UserDetails{Username: "john"}}, nil)
+			},
+			ExpectDetails: &authentication.UserDetailsExtended{GivenName: "John", UserDetails: &authentication.UserDetails{Username: "john"}},
 		},
 		{
 			Name:     "ShouldReturnErrorWhenGetDetailsFails",
@@ -185,7 +203,7 @@ func TestHandleVerifyGETAuthorizationBearerResolveUser(t *testing.T) {
 				tc.Setup(mock)
 			}
 
-			details, clientID, ccs, level, err := handleVerifyGETAuthorizationBearerResolveUser(mock.Ctx, tc.Username, tc.ClientID, tc.CCS, tc.Level)
+			details, clientID, ccs, level, err := handleVerifyGETAuthorizationBearerResolveUser(mock.Ctx, tc.Username, tc.ClientID, tc.CCS, tc.Level, tc.Extended)
 
 			if tc.ExpectError != "" {
 				require.EqualError(t, err, tc.ExpectError)
diff --git a/internal/handlers/handler_authz_test.go b/internal/handlers/handler_authz_test.go
index 3edc17b85..c060fe0fb 100644
--- a/internal/handlers/handler_authz_test.go
+++ b/internal/handlers/handler_authz_test.go
@@ -22,6 +22,7 @@ import (
 
 	"github.com/authelia/authelia/v4/internal/authentication"
 	"github.com/authelia/authelia/v4/internal/configuration/schema"
+	"github.com/authelia/authelia/v4/internal/expression"
 	"github.com/authelia/authelia/v4/internal/middlewares"
 	"github.com/authelia/authelia/v4/internal/mocks"
 	"github.com/authelia/authelia/v4/internal/model"
@@ -91,11 +92,11 @@ func (s *AuthzSuite) Builder() (builder *AuthzBuilder) {
 
 	switch s.implementation {
 	case AuthzImplExtAuthz:
-		return NewAuthzBuilder().WithImplementationExtAuthz()
+		return NewAuthzBuilder().WithImplementationExtAuthz().WithEndpointHeaders(schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameExtAuthz].Headers)
 	case AuthzImplForwardAuth:
-		return NewAuthzBuilder().WithImplementationForwardAuth()
+		return NewAuthzBuilder().WithImplementationForwardAuth().WithEndpointHeaders(schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameForwardAuth].Headers)
 	case AuthzImplAuthRequest:
-		return NewAuthzBuilder().WithImplementationAuthRequest()
+		return NewAuthzBuilder().WithImplementationAuthRequest().WithEndpointHeaders(schema.DefaultServerConfiguration.Endpoints.Authz[schema.AuthzEndpointNameAuthRequest].Headers)
 	case AuthzImplLegacy:
 		return NewAuthzBuilder().WithImplementationLegacy()
 	}
@@ -1569,6 +1570,167 @@ func (s *AuthzSuite) TestShouldNotFailOnMissingEmail() {
 	s.Equal("abc,123", string(mock.Ctx.Response.Header.PeekBytes(headerRemoteGroups)))
 }
 
+func (s *AuthzSuite) TestShouldSetHeadersFromExtendedUserAttributes() {
+	if s.setRequest == nil || s.implementation == AuthzImplLegacy {
+		s.T().Skip()
+	}
+
+	mock := mocks.NewMockAutheliaCtx(s.T())
+
+	defer mock.Close()
+
+	setUpMockClock(mock)
+
+	authz := s.Builder().WithConfig(&mock.Ctx.Configuration).WithEndpointHeaders(map[string]schema.ServerEndpointsAuthzHeader{
+		schema.HeaderRemoteUser: {UserAttribute: expression.AttributeUserUsername},
+		"Remote-Given-Name":     {UserAttribute: expression.AttributeUserGivenName},
+		"Remote-Teams":          {UserAttribute: "teams"},
+		"Remote-Employee-Id":    {UserAttribute: "employee_id"},
+		"Remote-Contractor":     {UserAttribute: "contractor"},
+		"Remote-Unknown":        {UserAttribute: "unknown"},
+	}).Build()
+
+	targetURI := s.RequireParseRequestURI("https://bypass.example.com")
+
+	s.setRequest(mock.Ctx, fasthttp.MethodGet, targetURI, true, false)
+
+	userSession, err := mock.Ctx.GetSession()
+	s.Require().NoError(err)
+
+	userSession.Username = testUsername
+	userSession.DisplayName = "John Smith"
+	userSession.Groups = []string{"admins", "dev"}
+	userSession.Emails = []string{"john@example.com"}
+	userSession.AuthenticationMethodRefs.UsernameAndPassword = true
+	userSession.RefreshTTL = mock.Clock.Now().Add(5 * time.Minute)
+
+	s.Require().NoError(mock.Ctx.SaveSession(userSession))
+
+	mock.UserProviderMock.EXPECT().
+		GetDetailsExtended(gomock.Eq(testUsername)).
+		Return(&authentication.UserDetailsExtended{
+			GivenName: "John",
+			UserDetails: &authentication.UserDetails{
+				Username:    testUsername,
+				DisplayName: "John Smith",
+				Groups:      []string{"admins", "dev"},
+				Emails:      []string{"john@example.com"},
+			},
+			Extra: map[string]any{
+				"teams":       []any{"devs", "ops"},
+				"employee_id": float64(10000000),
+				"contractor":  false,
+			},
+		}, nil).Times(1)
+
+	authz.Handler(mock.Ctx)
+
+	s.Equal(fasthttp.StatusOK, mock.Ctx.Response.StatusCode())
+	s.Equal(testUsername, string(mock.Ctx.Response.Header.PeekBytes(headerRemoteUser)))
+	s.Equal("John", string(mock.Ctx.Response.Header.Peek("Remote-Given-Name")))
+	s.Equal("devs,ops", string(mock.Ctx.Response.Header.Peek("Remote-Teams")))
+	s.Equal("10000000", string(mock.Ctx.Response.Header.Peek("Remote-Employee-Id")))
+	s.Equal("false", string(mock.Ctx.Response.Header.Peek("Remote-Contractor")))
+	s.Equal("", string(mock.Ctx.Response.Header.Peek("Remote-Unknown")))
+}
+
+func (s *AuthzSuite) TestShouldNotAuthenticateWhenExtendedUserDetailsAreEmpty() {
+	if s.setRequest == nil || s.implementation == AuthzImplLegacy {
+		s.T().Skip()
+	}
+
+	testCases := []struct {
+		name    string
+		details *authentication.UserDetailsExtended
+	}{
+		{"ShouldHandleNil", nil},
+		{"ShouldHandleEmptyUsername", &authentication.UserDetailsExtended{UserDetails: &authentication.UserDetails{}}},
+	}
+
+	for _, tc := range testCases {
+		s.Run(tc.name, func() {
+			mock := mocks.NewMockAutheliaCtx(s.T())
+
+			defer mock.Close()
+
+			setUpMockClock(mock)
+
+			authz := s.Builder().WithConfig(&mock.Ctx.Configuration).WithEndpointHeaders(map[string]schema.ServerEndpointsAuthzHeader{
+				schema.HeaderRemoteUser: {UserAttribute: expression.AttributeUserUsername},
+				"Remote-Given-Name":     {UserAttribute: expression.AttributeUserGivenName},
+			}).Build()
+
+			targetURI := s.RequireParseRequestURI("https://bypass.example.com")
+
+			s.setRequest(mock.Ctx, fasthttp.MethodGet, targetURI, true, false)
+
+			userSession, err := mock.Ctx.GetSession()
+			s.Require().NoError(err)
+
+			userSession.Username = testUsername
+			userSession.AuthenticationMethodRefs.UsernameAndPassword = true
+			userSession.RefreshTTL = mock.Clock.Now().Add(5 * time.Minute)
+
+			s.Require().NoError(mock.Ctx.SaveSession(userSession))
+
+			mock.UserProviderMock.EXPECT().
+				GetDetailsExtended(gomock.Eq(testUsername)).
+				Return(tc.details, nil).Times(1)
+
+			authz.Handler(mock.Ctx)
+
+			s.Equal("", string(mock.Ctx.Response.Header.PeekBytes(headerRemoteUser)))
+			s.Equal("", string(mock.Ctx.Response.Header.Peek("Remote-Given-Name")))
+
+			userSession, err = mock.Ctx.GetSession()
+			s.Require().NoError(err)
+
+			s.Equal("", userSession.Username)
+		})
+	}
+}
+
+func (s *AuthzSuite) TestShouldNotRetrieveUserDetailsWhenHeadersOnlyRequireSessionAttributes() {
+	if s.setRequest == nil {
+		s.T().Skip()
+	}
+
+	mock := mocks.NewMockAutheliaCtx(s.T())
+
+	defer mock.Close()
+
+	setUpMockClock(mock)
+
+	authz := s.Builder().WithConfig(&mock.Ctx.Configuration).Build()
+
+	targetURI := s.RequireParseRequestURI("https://bypass.example.com")
+
+	s.setRequest(mock.Ctx, fasthttp.MethodGet, targetURI, true, false)
+
+	userSession, err := mock.Ctx.GetSession()
+	s.Require().NoError(err)
+
+	userSession.Username = testUsername
+	userSession.DisplayName = "John Smith"
+	userSession.Groups = []string{"admins", "dev"}
+	userSession.Emails = []string{"john@example.com"}
+	userSession.AuthenticationMethodRefs.UsernameAndPassword = true
+	userSession.RefreshTTL = mock.Clock.Now().Add(5 * time.Minute)
+
+	s.Require().NoError(mock.Ctx.SaveSession(userSession))
+
+	mock.UserProviderMock.EXPECT().GetDetails(gomock.Any()).Times(0)
+	mock.UserProviderMock.EXPECT().GetDetailsExtended(gomock.Any()).Times(0)
+
+	authz.Handler(mock.Ctx)
+
+	s.Equal(fasthttp.StatusOK, mock.Ctx.Response.StatusCode())
+	s.Equal(testUsername, string(mock.Ctx.Response.Header.PeekBytes(headerRemoteUser)))
+	s.Equal("John Smith", string(mock.Ctx.Response.Header.PeekBytes(headerRemoteName)))
+	s.Equal("admins,dev", string(mock.Ctx.Response.Header.PeekBytes(headerRemoteGroups)))
+	s.Equal("john@example.com", string(mock.Ctx.Response.Header.PeekBytes(headerRemoteEmail)))
+}
+
 func (s *AuthzSuite) TestShouldApplyPolicyOfOneFactorDomain() {
 	if s.setRequest == nil {
 		s.T().Skip()
diff --git a/internal/handlers/handler_authz_types.go b/internal/handlers/handler_authz_types.go
index f2870c943..6d570c4a7 100644
--- a/internal/handlers/handler_authz_types.go
+++ b/internal/handlers/handler_authz_types.go
@@ -34,13 +34,21 @@ type Authz struct {
 	handleUnauthorized HandlerAuthzUnauthorized
 
 	implementation AuthzImplementation
+
+	headers []AuthzHeader
+}
+
+// AuthzHeader represents a response header which is set from a resolved user attribute.
+type AuthzHeader struct {
+	Key       []byte
+	Attribute string
 }
 
 // HandlerAuthzUnauthorized is a Authz handler func that handles unauthorized responses.
 type HandlerAuthzUnauthorized func(ctx AuthzContext, authn *Authn, redirectionURL *url.URL)
 
 // HandlerAuthzAuthorized is a Authz handler func that handles authorized responses.
-type HandlerAuthzAuthorized func(ctx AuthzContext, authn *Authn)
+type HandlerAuthzAuthorized func(ctx AuthzContext, headers []AuthzHeader, authn *Authn)
 
 // HandlerAuthzGetAutheliaURL is a Authz handler func that handles retrieval of the Portal URL.
 type HandlerAuthzGetAutheliaURL func(ctx AuthzContext) (portalURL *url.URL, err error)
@@ -77,7 +85,7 @@ type Authn struct {
 	Method   string
 	ClientID string
 
-	Details authentication.UserDetails
+	Details *authentication.UserDetailsExtended
 	Level   authentication.Level
 	Object  authorization.Object
 	Type    AuthnType
@@ -107,6 +115,7 @@ type AuthzBuilder struct {
 	config         AuthzConfig
 	implementation AuthzImplementation
 	strategies     []AuthnStrategy
+	headers        map[string]schema.ServerEndpointsAuthzHeader
 }
 
 // AuthnStrategy is a strategy used for Authz authentication.
diff --git a/internal/handlers/handler_authz_util.go b/internal/handlers/handler_authz_util.go
index 27bf6ad92..307c53dc8 100644
--- a/internal/handlers/handler_authz_util.go
+++ b/internal/handlers/handler_authz_util.go
@@ -7,15 +7,71 @@ package handlers
 import (
 	"fmt"
 	"net/url"
+	"strconv"
+	"strings"
+	"time"
 
 	"github.com/valyala/fasthttp"
 
 	"github.com/authelia/authelia/v4/internal/authentication"
 	"github.com/authelia/authelia/v4/internal/authorization"
+	"github.com/authelia/authelia/v4/internal/expression"
 	"github.com/authelia/authelia/v4/internal/session"
 	"github.com/authelia/authelia/v4/internal/utils"
 )
 
+var authzSessionUserAttributes = []string{
+	expression.AttributeUserUsername,
+	expression.AttributeUserGroups,
+	expression.AttributeUserDisplayName,
+	expression.AttributeUserEmail,
+	expression.AttributeUserEmails,
+	expression.AttributeUserEmailsExtra,
+	expression.AttributeUserEmailVerified,
+	expression.AttributeUserUpdatedAt,
+}
+
+func authzHeadersRequireExtendedUserDetails(headers []AuthzHeader) (extended bool) {
+	for _, header := range headers {
+		if !utils.IsStringInSlice(header.Attribute, authzSessionUserAttributes) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func authzHeaderValue(object any) (value string) {
+	switch v := object.(type) {
+	case nil:
+		return ""
+	case string:
+		return v
+	case []string:
+		return strings.Join(v, ",")
+	case []any:
+		values := make([]string, len(v))
+
+		for i, item := range v {
+			values[i] = authzHeaderValue(item)
+		}
+
+		return strings.Join(values, ",")
+	case bool:
+		return strconv.FormatBool(v)
+	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64:
+		return fmt.Sprintf("%d", v)
+	case float32:
+		return strconv.FormatFloat(float64(v), 'f', -1, 32)
+	case float64:
+		return strconv.FormatFloat(v, 'f', -1, 64)
+	case time.Time:
+		return v.Format(time.RFC3339)
+	default:
+		return fmt.Sprintf("%v", v)
+	}
+}
+
 func friendlyMethod(m string) (fm string) {
 	switch m {
 	case "":
diff --git a/internal/handlers/handler_authz_util_test.go b/internal/handlers/handler_authz_util_test.go
index 8ed9706cb..84ea6102b 100644
--- a/internal/handlers/handler_authz_util_test.go
+++ b/internal/handlers/handler_authz_util_test.go
@@ -7,12 +7,15 @@ package handlers
 import (
 	"net/url"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/valyala/fasthttp"
 
 	"github.com/authelia/authelia/v4/internal/authorization"
+	"github.com/authelia/authelia/v4/internal/configuration/schema"
+	"github.com/authelia/authelia/v4/internal/expression"
 	"github.com/authelia/authelia/v4/internal/mocks"
 )
 
@@ -372,3 +375,148 @@ func TestGetSafeAutheliaURL(t *testing.T) {
 		})
 	}
 }
+
+func TestAuthzHeaderValue(t *testing.T) {
+	testCases := []struct {
+		Name     string
+		Have     any
+		Expected string
+	}{
+		{
+			Name:     "ShouldHandleNil",
+			Have:     nil,
+			Expected: "",
+		},
+		{
+			Name:     "ShouldHandleString",
+			Have:     "john",
+			Expected: "john",
+		},
+		{
+			Name:     "ShouldJoinStringSlice",
+			Have:     []string{"admins", "dev"},
+			Expected: "admins,dev",
+		},
+		{
+			Name:     "ShouldJoinEmptyStringSlice",
+			Have:     []string{},
+			Expected: "",
+		},
+		{
+			Name:     "ShouldJoinAnySliceOfStrings",
+			Have:     []any{"admins", "dev"},
+			Expected: "admins,dev",
+		},
+		{
+			Name:     "ShouldJoinAnySliceOfMixedValues",
+			Have:     []any{"admins", 5, true, nil, 1.5},
+			Expected: "admins,5,true,,1.5",
+		},
+		{
+			Name:     "ShouldHandleBool",
+			Have:     false,
+			Expected: "false",
+		},
+		{
+			Name:     "ShouldHandleInt",
+			Have:     10000000,
+			Expected: "10000000",
+		},
+		{
+			Name:     "ShouldHandleInt64",
+			Have:     int64(-5),
+			Expected: "-5",
+		},
+		{
+			Name:     "ShouldHandleUint",
+			Have:     uint(5),
+			Expected: "5",
+		},
+		{
+			Name:     "ShouldHandleFloat64WithoutScientificNotation",
+			Have:     float64(10000000),
+			Expected: "10000000",
+		},
+		{
+			Name:     "ShouldHandleFloat64WithFraction",
+			Have:     1.5,
+			Expected: "1.5",
+		},
+		{
+			Name:     "ShouldHandleFloat32",
+			Have:     float32(1.5),
+			Expected: "1.5",
+		},
+		{
+			Name:     "ShouldHandleTime",
+			Have:     time.Date(2026, 9, 12, 17, 0, 0, 0, time.UTC),
+			Expected: "2026-09-12T17:00:00Z",
+		},
+		{
+			Name:     "ShouldFallbackToDefaultFormatting",
+			Have:     map[string]string{"abc": "123"},
+			Expected: "map[abc:123]",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.Name, func(t *testing.T) {
+			assert.Equal(t, tc.Expected, authzHeaderValue(tc.Have))
+		})
+	}
+}
+
+func TestAuthzHeadersRequireExtendedUserDetails(t *testing.T) {
+	testCases := []struct {
+		Name     string
+		Have     []AuthzHeader
+		Expected bool
+	}{
+		{
+			Name:     "ShouldNotRequireExtendedForNoHeaders",
+			Have:     nil,
+			Expected: false,
+		},
+		{
+			Name: "ShouldNotRequireExtendedForDefaultHeaders",
+			Have: []AuthzHeader{
+				{Key: []byte(schema.HeaderRemoteUser), Attribute: expression.AttributeUserUsername},
+				{Key: []byte(schema.HeaderRemoteGroups), Attribute: expression.AttributeUserGroups},
+				{Key: []byte(schema.HeaderRemoteName), Attribute: expression.AttributeUserDisplayName},
+				{Key: []byte(schema.HeaderRemoteEmail), Attribute: expression.AttributeUserEmail},
+			},
+			Expected: false,
+		},
+		{
+			Name: "ShouldNotRequireExtendedForOtherSessionAttributes",
+			Have: []AuthzHeader{
+				{Key: []byte("Remote-Emails"), Attribute: expression.AttributeUserEmails},
+				{Key: []byte("Remote-Emails-Extra"), Attribute: expression.AttributeUserEmailsExtra},
+				{Key: []byte("Remote-Email-Verified"), Attribute: expression.AttributeUserEmailVerified},
+				{Key: []byte("Remote-Updated-At"), Attribute: expression.AttributeUserUpdatedAt},
+			},
+			Expected: false,
+		},
+		{
+			Name: "ShouldRequireExtendedForStandardExtendedAttribute",
+			Have: []AuthzHeader{
+				{Key: []byte(schema.HeaderRemoteUser), Attribute: expression.AttributeUserUsername},
+				{Key: []byte("Remote-Given-Name"), Attribute: expression.AttributeUserGivenName},
+			},
+			Expected: true,
+		},
+		{
+			Name: "ShouldRequireExtendedForCustomAttribute",
+			Have: []AuthzHeader{
+				{Key: []byte("Remote-Teams"), Attribute: "teams"},
+			},
+			Expected: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.Name, func(t *testing.T) {
+			assert.Equal(t, tc.Expected, authzHeadersRequireExtendedUserDetails(tc.Have))
+		})
+	}
+}
diff --git a/internal/middlewares/authelia_context.go b/internal/middlewares/authelia_context.go
index b5dc05886..0f386b718 100644
--- a/internal/middlewares/authelia_context.go
+++ b/internal/middlewares/authelia_context.go
@@ -647,7 +647,7 @@ func (ctx *AutheliaCtx) SpecialRedirect(uri string, statusCode int) {
 	u, statusCode = ctx.setSpecialRedirect(uri, statusCode)
 
 	ctx.SetContentTypeTextHTML()
-	ctx.SetBodyString(fmt.Sprintf("<a href=\"%s\">%d %s</a>", utils.StringHTMLEscape(string(u)), statusCode, fasthttp.StatusMessage(statusCode)))
+	ctx.SetBodyString(fmt.Sprintf(`<a href="%s">%d %s</a>`, utils.StringHTMLEscape(string(u)), statusCode, fasthttp.StatusMessage(statusCode)))
 }
 
 // SpecialRedirectNoBody performs a redirect similar to fasthttp.RequestCtx except it allows statusCode 401 and includes
diff --git a/internal/mocks/authelia_context.go b/internal/mocks/authelia_context.go
index c9a205390..ec02ddabe 100644
--- a/internal/mocks/authelia_context.go
+++ b/internal/mocks/authelia_context.go
@@ -23,6 +23,7 @@ import (
 	"github.com/authelia/authelia/v4/internal/authorization"
 	"github.com/authelia/authelia/v4/internal/clock"
 	"github.com/authelia/authelia/v4/internal/configuration/schema"
+	"github.com/authelia/authelia/v4/internal/expression"
 	"github.com/authelia/authelia/v4/internal/middlewares"
 	"github.com/authelia/authelia/v4/internal/random"
 	"github.com/authelia/authelia/v4/internal/regulation"
@@ -213,6 +214,8 @@ func NewMockAutheliaCtx(t *testing.T) *MockAutheliaCtx {
 	providers.Authorizer = authorization.NewAuthorizer(
 		&config)
 
+	providers.UserAttributeResolver = expression.NewUserAttributes(&config)
+
 	providers.SessionProvider = session.NewProvider(config.Session, nil)
 
 	providers.Regulator = regulation.NewRegulator(config.Regulation, providers.StorageProvider, &mockAuthelia.Clock)
diff --git a/internal/suites/Standalone/configuration.yml b/internal/suites/Standalone/configuration.yml
index 15d19af04..7fb85f4a7 100644
--- a/internal/suites/Standalone/configuration.yml
+++ b/internal/suites/Standalone/configuration.yml
@@ -21,6 +21,28 @@ server:
         - 'session'
         - 'user'
       cache: '0'
+    authz:
+      legacy:
+        implementation: 'Legacy'
+      auth-request:
+        implementation: 'AuthRequest'
+      ext-authz:
+        implementation: 'ExtAuthz'
+      forward-auth:
+        implementation: 'ForwardAuth'
+      forward-auth-attributes:
+        implementation: 'ForwardAuth'
+        headers:
+          Remote-User:
+            user_attribute: 'username'
+          Remote-Groups:
+            user_attribute: 'groups'
+          Remote-Given-Name:
+            user_attribute: 'given_name'
+          Remote-Employee-Id:
+            user_attribute: 'employee_id'
+          Remote-Is-Admin:
+            user_attribute: 'is_admin'
     rate_limits:
       reset_password_start:
         buckets:
@@ -95,6 +117,14 @@ session:
 authentication_backend:
   file:
     path: '/config/users.yml'
+    extra_attributes:
+      employee_id:
+        value_type: 'integer'
+
+definitions:
+  user_attributes:
+    is_admin:
+      expression: '"admins" in groups'
 
 totp:
   issuer: 'example.com'
diff --git a/internal/suites/Standalone/users.yml b/internal/suites/Standalone/users.yml
index 5b0bbd6e5..d83c1fef7 100644
--- a/internal/suites/Standalone/users.yml
+++ b/internal/suites/Standalone/users.yml
@@ -8,9 +8,12 @@ users:
     displayname: "John Doe"
     password: "$6$rounds=500000$jgiCMRyGXzoqpxS3$w2pJeZnnH8bwW3zzvoMWtTRfQYsHbWbD/hquuQ5vUeIyl9gdwBIt6RWk2S6afBA0DPakbeWgD/4SZPiS0hYtU/"  # yamllint disable-line rule:line-length
     email: john.doe@authelia.com
+    given_name: "John"
     groups:
       - admins
       - dev
+    extra:
+      employee_id: 1001
 
   harry:
     displayname: "Harry Potter"
diff --git a/internal/suites/suite_standalone_test.go b/internal/suites/suite_standalone_test.go
index 0033fb820..561067ec5 100644
--- a/internal/suites/suite_standalone_test.go
+++ b/internal/suites/suite_standalone_test.go
@@ -12,6 +12,7 @@ import (
 	"log"
 	"net/http"
 	"net/url"
+	"strings"
 	"testing"
 	"time"
 
@@ -296,6 +297,82 @@ func (s *StandaloneSuite) TestShouldVerifyAPIVerifyRedirectFromXOriginalHostURI(
 	s.Assert().Equal(fmt.Sprintf("<a href=\"%s\">302 Found</a>", utils.StringHTMLEscape(fmt.Sprintf("%s/?rd=%s&rm=GET", GetLoginBaseURL(BaseDomain), urlEncodedAdminURL))), string(body))
 }
 
+func (s *StandaloneSuite) doAuthzBasicRequest(endpoint, username, password string) *http.Response {
+	req, err := http.NewRequest(fasthttp.MethodGet, fmt.Sprintf("%s/api/authz/%s", AutheliaBaseURL, endpoint), nil)
+	s.Require().NoError(err)
+
+	req.Header.Set("X-Forwarded-Method", fasthttp.MethodGet)
+	req.Header.Set(fasthttp.HeaderXForwardedProto, "https")
+	req.Header.Set(fasthttp.HeaderXForwardedHost, fmt.Sprintf("singlefactor.%s", BaseDomain))
+	req.Header.Set("X-Forwarded-URI", "/")
+	req.Header.Set(fasthttp.HeaderAccept, "text/html; charset=utf8")
+
+	if username != "" {
+		req.SetBasicAuth(username, password)
+	}
+
+	res, err := NewHTTPClient().Do(req)
+	s.Require().NoError(err)
+
+	s.T().Cleanup(func() {
+		_ = res.Body.Close()
+	})
+
+	return res
+}
+
+func (s *StandaloneSuite) TestShouldRespondWithDefaultAuthzHeaders() {
+	res := s.doAuthzBasicRequest("forward-auth", "john", "password")
+
+	s.Require().Equal(fasthttp.StatusOK, res.StatusCode)
+
+	s.Assert().Equal("john", res.Header.Get("Remote-User"))
+	s.Assert().ElementsMatch([]string{"admins", "dev"}, strings.Split(res.Header.Get("Remote-Groups"), ","))
+	s.Assert().Equal("John Doe", res.Header.Get("Remote-Name"))
+	s.Assert().Equal("john.doe@authelia.com", res.Header.Get("Remote-Email"))
+
+	s.Assert().Empty(res.Header.Values("Remote-Given-Name"))
+	s.Assert().Empty(res.Header.Values("Remote-Employee-Id"))
+	s.Assert().Empty(res.Header.Values("Remote-Is-Admin"))
+}
+
+func (s *StandaloneSuite) TestShouldRespondWithConfiguredAuthzHeaders() {
+	res := s.doAuthzBasicRequest("forward-auth-attributes", "john", "password")
+
+	s.Require().Equal(fasthttp.StatusOK, res.StatusCode)
+
+	s.Assert().Equal("john", res.Header.Get("Remote-User"))
+	s.Assert().ElementsMatch([]string{"admins", "dev"}, strings.Split(res.Header.Get("Remote-Groups"), ","))
+	s.Assert().Equal("John", res.Header.Get("Remote-Given-Name"))
+	s.Assert().Equal("1001", res.Header.Get("Remote-Employee-Id"))
+	s.Assert().Equal("true", res.Header.Get("Remote-Is-Admin"))
+
+	s.Assert().Empty(res.Header.Values("Remote-Name"))
+	s.Assert().Empty(res.Header.Values("Remote-Email"))
+}
+
+func (s *StandaloneSuite) TestShouldRespondWithConfiguredAuthzHeadersForUserWithoutAttributes() {
+	res := s.doAuthzBasicRequest("forward-auth-attributes", "harry", "password")
+
+	s.Require().Equal(fasthttp.StatusOK, res.StatusCode)
+
+	s.Assert().Equal("harry", res.Header.Get("Remote-User"))
+	s.Assert().Equal("", res.Header.Get("Remote-Groups"))
+	s.Assert().Equal("", res.Header.Get("Remote-Given-Name"))
+	s.Assert().Equal("", res.Header.Get("Remote-Employee-Id"))
+	s.Assert().Equal("false", res.Header.Get("Remote-Is-Admin"))
+}
+
+func (s *StandaloneSuite) TestShouldNotRespondWithConfiguredAuthzHeadersWhenUnauthenticated() {
+	res := s.doAuthzBasicRequest("forward-auth-attributes", "", "")
+
+	s.Assert().Equal(fasthttp.StatusFound, res.StatusCode)
+
+	for _, header := range []string{"Remote-User", "Remote-Groups", "Remote-Given-Name", "Remote-Employee-Id", "Remote-Is-Admin"} {
+		s.Assert().Empty(res.Header.Values(header), header)
+	}
+}
+
 func (s *StandaloneSuite) TestShouldServeVerboseHealthCheck() {
 	client := NewHTTPClient()