#942 Add the SignedOutCallbackRedirect event for OIDC

src/Microsoft.AspNetCore.Authentication.OpenIdConnect/Events/OpenIdConnectEvents.cs

@@ -38,6 +38,11 @@ namespace Microsoft.AspNetCore.Authentication.OpenIdConnect
         /// </summary>
         public Func<RedirectContext, Task> OnRedirectToIdentityProviderForSignOut { get; set; } = context => Task.CompletedTask;
 
+        /// <summary>
+        /// Invoked before redirecting to the <see cref="OpenIdConnectOptions.SignedOutRedirectUri"/> at the end of a remote sign-out flow.
+        /// </summary>
+        public Func<RemoteSignOutContext, Task> OnSignedOutCallbackRedirect { get; set; } = context => Task.CompletedTask;
+
         /// <summary>
         /// Invoked when a request is received on the RemoteSignOutPath.
         /// </summary>
@@ -68,6 +73,8 @@ namespace Microsoft.AspNetCore.Authentication.OpenIdConnect
 
         public virtual Task RedirectToIdentityProviderForSignOut(RedirectContext context) => OnRedirectToIdentityProviderForSignOut(context);
 
+        public virtual Task SignedOutCallbackRedirect(RemoteSignOutContext context) => OnSignedOutCallbackRedirect(context);
+
         public virtual Task RemoteSignOut(RemoteSignOutContext context) => OnRemoteSignOut(context);
 
         public virtual Task TokenResponseReceived(TokenResponseReceivedContext context) => OnTokenResponseReceived(context);

src/Microsoft.AspNetCore.Authentication.OpenIdConnect/LoggingExtensions.cs

@@ -9,6 +9,8 @@ namespace Microsoft.Extensions.Logging
     {
         private static Action<ILogger, Exception> _redirectToIdentityProviderForSignOutHandledResponse;
         private static Action<ILogger, Exception> _redirectToIdentityProviderHandledResponse;
+        private static Action<ILogger, Exception> _signoutCallbackRedirectHandledResponse;
+        private static Action<ILogger, Exception> _signoutCallbackRedirectSkipped;
         private static Action<ILogger, Exception> _updatingConfiguration;
         private static Action<ILogger, Exception> _receivedIdToken;
         private static Action<ILogger, Exception> _redeemingCodeForTokens;
@@ -248,6 +250,14 @@ namespace Microsoft.Extensions.Logging
                  eventId: 49,
                  logLevel: LogLevel.Information,
                  formatString: "AuthenticationScheme: {AuthenticationScheme} signed out.");
+            _signoutCallbackRedirectHandledResponse = LoggerMessage.Define(
+                eventId: 50,
+                logLevel: LogLevel.Debug,
+                formatString: "RedirectToSignedOutRedirectUri.HandledResponse");
+            _signoutCallbackRedirectSkipped = LoggerMessage.Define(
+                eventId: 51,
+                logLevel: LogLevel.Debug,
+                formatString: "RedirectToSignedOutRedirectUri.Skipped");
         }
 
         public static void UpdatingConfiguration(this ILogger logger)
@@ -345,6 +355,16 @@ namespace Microsoft.Extensions.Logging
             _redirectToIdentityProviderHandledResponse(logger, null);
         }
 
+        public static void SignoutCallbackRedirectHandledResponse(this ILogger logger)
+        {
+            _signoutCallbackRedirectHandledResponse(logger, null);
+        }
+
+        public static void SignoutCallbackRedirectSkipped(this ILogger logger)
+        {
+            _signoutCallbackRedirectSkipped(logger, null);
+        }
+
         public static void UserInformationReceivedHandledResponse(this ILogger logger)
         {
             _userInformationReceivedHandledResponse(logger, null);

src/Microsoft.AspNetCore.Authentication.OpenIdConnect/OpenIdConnectHandler.cs

@@ -122,6 +122,10 @@ namespace Microsoft.AspNetCore.Authentication.OpenIdConnect
                     Logger.RemoteSignOutSkipped();
                     return false;
                 }
+                if (remoteSignOutContext.Result.Failure != null)
+                {
+                    throw new InvalidOperationException("An error was returned from the RemoteSignOut event.", remoteSignOutContext.Result.Failure);
+                }
             }
 
             if (message == null)
@@ -273,18 +277,46 @@ namespace Microsoft.AspNetCore.Authentication.OpenIdConnect
         /// Response to the callback from OpenId provider after session ended.
         /// </summary>
         /// <returns>A task executing the callback procedure</returns>
-        protected virtual Task<bool> HandleSignOutCallbackAsync()
+        protected async virtual Task<bool> HandleSignOutCallbackAsync()
         {
-            if (Request.Query.TryGetValue(OpenIdConnectParameterNames.State, out StringValues protectedState))
+            var message = new OpenIdConnectMessage(Request.Query.Select(pair => new KeyValuePair<string, string[]>(pair.Key, pair.Value)));
+            AuthenticationProperties properties = null;
+            if (!string.IsNullOrEmpty(message.State))
             {
-                var properties = Options.StateDataFormat.Unprotect(protectedState);
+                properties = Options.StateDataFormat.Unprotect(message.State);
-                if (!string.IsNullOrEmpty(properties?.RedirectUri))
+            }
+
+            var signOut = new RemoteSignOutContext(Context, Scheme, Options, message)
+            {
+                Properties = properties,
+            };
+
+            await Events.SignedOutCallbackRedirect(signOut);
+            if (signOut.Result != null)
+            {
+                if (signOut.Result.Handled)
                 {
-                    Response.Redirect(properties.RedirectUri);
+                    Logger.SignoutCallbackRedirectHandledResponse();
+                    return true;
+                }
+                if (signOut.Result.Skipped)
+                {
+                    Logger.SignoutCallbackRedirectSkipped();
+                    return false;
+                }
+                if (signOut.Result.Failure != null)
+                {
+                    throw new InvalidOperationException("An error was returned from the SignedOutCallbackRedirect event.", signOut.Result.Failure);
                 }
             }
 
-            return Task.FromResult(true);
+            properties = signOut.Properties;
+            if (!string.IsNullOrEmpty(properties?.RedirectUri))
+            {
+                Response.Redirect(properties.RedirectUri);
+            }
+
+            return true;
         }
 
         /// <summary>

src/Microsoft.AspNetCore.Authentication/RemoteAuthenticationHandler.cs

@@ -93,6 +93,10 @@ namespace Microsoft.AspNetCore.Authentication
                     {
                         return false;
                     }
+                    else if (errorContext.Result.Failure != null)
+                    {
+                        throw new InvalidOperationException("An error was returned from the RemoteFailure event.", errorContext.Result.Failure);
+                    }
                 }
 
                 throw exception;