add option for ui_localales query param for proper login page localization

src/Keycloak.IdentityModel/Models/Configuration/DefaultKeycloakParameters.cs

@@ -164,6 +164,18 @@ public class DefaultKeycloakParameters : IKeycloakParameters
         ///     - Default: If not specified, an exception will be thrown if and error from Keycloak authentication is received.
         /// </remarks>
         public string AuthResponseErrorRedirectUrl { get; set; }
+        /// <summary>
+        /// OPTIONAL: Query param for login page in order to get the desired locale login page, sending ui_locales query parameter
+        /// By default keycloak will server the login page in this priority
+        /// 1. kc_locale query parameter
+        /// 2. KEYCLOAK_LOCALE cookie value
+        /// 3. User’s preferred locale if a user instance is available
+        /// 4. ui_locales query parameter
+        /// 5. Accept-Language request header
+        /// 6. Realm’s default language
+        /// </summary>
+
+        public string UiLocales { get; set; }
 
     }
 }

src/Keycloak.IdentityModel/Models/Configuration/IKeycloakSettings.cs

@@ -23,5 +23,7 @@ public interface IKeycloakParameters
         bool DisableRefreshTokenSignatureValidation { get; }
         bool DisableAllRefreshTokenValidation { get; }
         string AuthResponseErrorRedirectUrl { get; }
+
+        string UiLocales { get; set; }
     }
 }

src/Keycloak.IdentityModel/Utilities/OidcDataManager.cs

@@ -278,6 +278,9 @@ public HttpContent BuildAuthorizationEndpointContent(Uri requestUri, string stat
             if (!string.IsNullOrWhiteSpace(_options.IdentityProvider))
                 parameters.Add(Constants.KeycloakParameters.IdpHint, _options.IdentityProvider);
 
+            if (!string.IsNullOrWhiteSpace(_options.UiLocales))
+                parameters.Add(Protocols.OpenIdConnectParameterNames.UiLocales, _options.UiLocales);
+
             return new FormUrlEncodedContent(parameters);
         }
 

src/Owin.Security.Keycloak/Configuration/KeycloakAuthenticationOptions.cs

@@ -226,5 +226,16 @@ public KeycloakAuthenticationOptions()
         /// </remarks>
         public string AuthResponseErrorRedirectUrl { get; set; }
 
+        /// <summary>
+        /// OPTIONAL: Query param for login page in order to get the desired locale login page, sending ui_locales query parameter
+        /// By default keycloak will server the login page in this priority
+        /// 1. kc_locale query parameter
+        /// 2. KEYCLOAK_LOCALE cookie value
+        /// 3. User’s preferred locale if a user instance is available
+        /// 4. ui_locales query parameter
+        /// 5. Accept-Language request header
+        /// 6. Realm’s default language
+        /// </summary>
+        public string UiLocales { get; set; }
     }
-}
+}