Add AdditionalAuthorizationParameters to OAuthOptions/OpenIdConnectOptions

src/Security/Authentication/OAuth/src/OAuthHandler.cs

@@ -303,12 +303,12 @@ protected virtual string BuildChallengeUrl(AuthenticationProperties properties,
         var scope = scopeParameter != null ? FormatScope(scopeParameter) : FormatScope();
 
         var parameters = new Dictionary<string, string>
-            {
-                { "client_id", Options.ClientId },
-                { "scope", scope },
-                { "response_type", "code" },
-                { "redirect_uri", redirectUri },
-            };
+        {
+            { "client_id", Options.ClientId },
+            { "scope", scope },
+            { "response_type", "code" },
+            { "redirect_uri", redirectUri },
+        };
 
         if (Options.UsePkce)
         {
@@ -328,6 +328,11 @@ protected virtual string BuildChallengeUrl(AuthenticationProperties properties,
 
         parameters["state"] = Options.StateDataFormat.Protect(properties);
 
+        foreach (var additionalParameter in Options.AdditionalAuthorizationParameters)
+        {
+            parameters.Add(additionalParameter.Key, additionalParameter.Value);
+        }
+
         return QueryHelpers.AddQueryString(Options.AuthorizationEndpoint, parameters!);
     }
 

src/Security/Authentication/OAuth/src/OAuthOptions.cs

@@ -83,6 +83,16 @@ public override void Validate()
     /// </summary>
     public ICollection<string> Scope { get; } = new HashSet<string>();
 
+    /// <summary>
+    /// Gets the additional parameters that will be included in the authorization request.
+    /// </summary>
+    /// <remarks>
+    /// The additional parameters can be used to customize the authorization request,
+    /// providing extra information or fulfilling specific requirements of the OAuth provider.
+    /// These parameters are typically, but not always, appended to the query string.
+    /// </remarks>
+    public IDictionary<string, string> AdditionalAuthorizationParameters { get; } = new Dictionary<string, string>();
+
     /// <summary>
     /// Gets or sets the type used to secure data handled by the middleware.
     /// </summary>

src/Security/Authentication/OAuth/src/PublicAPI.Unshipped.txt

@@ -1 +1,2 @@
 #nullable enable
+Microsoft.AspNetCore.Authentication.OAuth.OAuthOptions.AdditionalAuthorizationParameters.get -> System.Collections.Generic.IDictionary<string!, string!>!

src/Security/Authentication/OpenIdConnect/src/OpenIdConnectHandler.cs

@@ -450,6 +450,11 @@ private async Task HandleChallengeAsyncInternal(AuthenticationProperties propert
 
         GenerateCorrelationId(properties);
 
+        foreach (var additionalParameter in Options.AdditionalAuthorizationParameters)
+        {
+            message.Parameters.Add(additionalParameter.Key, additionalParameter.Value);
+        }
+
         var redirectContext = new RedirectContext(Context, Scheme, Options, properties)
         {
             ProtocolMessage = message

src/Security/Authentication/OpenIdConnect/src/OpenIdConnectOptions.cs

@@ -236,6 +236,16 @@ public override void Validate()
     /// </summary>
     public ICollection<string> Scope { get; } = new HashSet<string>();
 
+    /// <summary>
+    /// Gets the additional parameters that will be included in the authorization request.
+    /// </summary>
+    /// <remarks>
+    /// The additional parameters can be used to customize the authorization request,
+    /// providing extra information or fulfilling specific requirements of the OpenIdConnect provider.
+    /// These parameters are typically, but not always, appended to the query string.
+    /// </remarks>
+    public IDictionary<string, string> AdditionalAuthorizationParameters { get; } = new Dictionary<string, string>();
+
     /// <summary>
     /// Requests received on this path will cause the handler to invoke SignOut using the SignOutScheme.
     /// </summary>

src/Security/Authentication/OpenIdConnect/src/PublicAPI.Unshipped.txt

@@ -1 +1,2 @@
 #nullable enable
+Microsoft.AspNetCore.Authentication.OpenIdConnect.OpenIdConnectOptions.AdditionalAuthorizationParameters.get -> System.Collections.Generic.IDictionary<string!, string!>!

src/Security/Authentication/test/OAuthTests.cs

@@ -193,6 +193,32 @@ public async Task RedirectToAuthorizeEndpoint_HasScopeAsConfigured()
         Assert.Contains("scope=foo%20bar", res.Headers.Location.Query);
     }
 
+    [Fact]
+    public async Task RedirectToAuthorizeEndpoint_HasAdditionalAuthorizationParametersAsConfigured()
+    {
+        using var host = await CreateHost(
+            s => s.AddAuthentication(o => o.DisableAutoDefaultScheme = true).AddOAuth(
+                "Weblie",
+                opt =>
+                {
+                    ConfigureDefaults(opt);
+                    opt.AdditionalAuthorizationParameters.Add("prompt", "login");
+                    opt.AdditionalAuthorizationParameters.Add("audience", "https://api.example.com");
+                }),
+            async ctx =>
+            {
+                await ctx.ChallengeAsync("Weblie");
+                return true;
+            });
+
+        using var server = host.GetTestServer();
+        var transaction = await server.SendAsync("https://www.example.com/challenge");
+        var res = transaction.Response;
+
+        Assert.Equal(HttpStatusCode.Redirect, res.StatusCode);
+        Assert.Contains("prompt=login&audience=https%3A%2F%2Fapi.example.com", res.Headers.Location.Query);
+    }
+
     [Fact]
     public async Task RedirectToAuthorizeEndpoint_HasScopeAsOverwritten()
     {

src/Security/Authentication/test/OpenIdConnect/OpenIdConnectChallengeTests.cs

@@ -670,4 +670,25 @@ public async Task Challenge_HasOverwrittenMaxAgeParaFromBaseAuthenticationProper
         settings.ValidateChallengeRedirect(res.Headers.Location);
         Assert.Contains("max_age=1234", res.Headers.Location.Query);
     }
+
+    [Fact]
+    public async Task Challenge_WithAdditionalAuthorizationParameters()
+    {
+        var settings = new TestSettings(opt =>
+        {
+            opt.ClientId = "Test Id";
+            opt.Authority = TestServerBuilder.DefaultAuthority;
+            opt.AdditionalAuthorizationParameters.Add("prompt", "login");
+            opt.AdditionalAuthorizationParameters.Add("audience", "https://api.example.com");
+        });
+
+        var server = settings.CreateTestServer();
+        var transaction = await server.SendAsync(TestServerBuilder.TestHost + TestServerBuilder.ChallengeWithProperties);
+
+        var res = transaction.Response;
+
+        Assert.Equal(HttpStatusCode.Redirect, res.StatusCode);
+        settings.ValidateChallengeRedirect(res.Headers.Location);
+        Assert.Contains("prompt=login&audience=https%3A%2F%2Fapi.example.com", res.Headers.Location.Query);
+    }
 }