Mark DynamicClientRegistrationOptions.ApplicationType as [Experimental] per SEP-837

Agent-Logs-Url: https://github.com/modelcontextprotocol/csharp-sdk/sessions/ef973045-314b-4c42-821b-c467c7a0e8e6

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

docs/list-of-diagnostics.md

@@ -23,7 +23,7 @@ If you use experimental APIs, you will get one of the diagnostics shown below. T
 
 | Diagnostic ID | Description |
 | :------------ | :---------- |
-| `MCPEXP001` | Experimental APIs for features in the MCP specification itself, including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [MCP Tasks specification](https://modelcontextprotocol.io/specification/draft/basic/utilities/tasks)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |
+| `MCPEXP001` | Experimental APIs for features in the MCP specification itself, including Tasks, Extensions, and the `application_type` parameter in Dynamic Client Registration. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [MCP Tasks specification](https://modelcontextprotocol.io/specification/draft/basic/utilities/tasks)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). The `application_type` parameter in Dynamic Client Registration is part of a future MCP specification version (see [SEP-837](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/837)). |
 | `MCPEXP002` | Experimental SDK APIs unrelated to the MCP specification itself, including subclassing `McpClient`/`McpServer` (see [#1363](https://github.com/modelcontextprotocol/csharp-sdk/pull/1363)) and `RunSessionHandler`, which may be removed or change signatures in a future release (consider using `ConfigureSessionOptions` instead). |
 
 ## Obsolete APIs

src/Common/Experimentals.cs

@@ -110,4 +110,23 @@ internal static class Experimentals
     /// URL for the experimental <c>RunSessionHandler</c> API.
     /// </summary>
     public const string RunSessionHandler_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcpexp002";
+
+    /// <summary>
+    /// Diagnostic ID for the experimental <c>application_type</c> parameter in Dynamic Client Registration per SEP-837.
+    /// </summary>
+    /// <remarks>
+    /// This uses the same diagnostic ID as <see cref="Tasks_DiagnosticId"/> because it is an experimental
+    /// feature in the MCP specification itself.
+    /// </remarks>
+    public const string DcrApplicationType_DiagnosticId = "MCPEXP001";
+
+    /// <summary>
+    /// Message for the experimental <c>application_type</c> parameter in Dynamic Client Registration.
+    /// </summary>
+    public const string DcrApplicationType_Message = "The application_type parameter in Dynamic Client Registration is part of a future MCP specification version (SEP-837) and is subject to change.";
+
+    /// <summary>
+    /// URL for the experimental <c>application_type</c> parameter in Dynamic Client Registration.
+    /// </summary>
+    public const string DcrApplicationType_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcpexp001";
 }

src/ModelContextProtocol.Core/Authentication/ClientOAuthProvider.cs

@@ -90,7 +90,9 @@ public ClientOAuthProvider(
         _dcrClientUri = options.DynamicClientRegistration?.ClientUri;
         _dcrInitialAccessToken = options.DynamicClientRegistration?.InitialAccessToken;
         _dcrResponseDelegate = options.DynamicClientRegistration?.ResponseDelegate;
+#pragma warning disable MCPEXP001 // application_type in DCR is experimental per SEP-837
         _dcrApplicationType = options.DynamicClientRegistration?.ApplicationType;
+#pragma warning restore MCPEXP001
         _tokenCache = options.TokenCache ?? new InMemoryTokenCache();
     }
 

src/ModelContextProtocol.Core/Authentication/DynamicClientRegistrationOptions.cs

@@ -1,3 +1,5 @@
+using System.Diagnostics.CodeAnalysis;
+
 namespace ModelContextProtocol.Authentication;
 
 /// <summary>
@@ -61,5 +63,6 @@ public sealed class DynamicClientRegistrationOptions
     /// should use "native", and web applications (remote browser-based) should use "web".
     /// </para>
     /// </remarks>
+    [Experimental(Experimentals.DcrApplicationType_DiagnosticId, UrlFormat = Experimentals.DcrApplicationType_Url)]
     public string? ApplicationType { get; set; }
 }

tests/ModelContextProtocol.AspNetCore.Tests/OAuth/AuthTests.cs

@@ -1313,6 +1313,7 @@ public async Task DynamicClientRegistration_SendsWebApplicationType_ForNonLocalh
     }
 
     [Fact]
+#pragma warning disable MCPEXP001 // application_type in DCR is experimental per SEP-837
     public async Task DynamicClientRegistration_UsesExplicitApplicationType_WhenConfigured()
     {
         await using var app = await StartMcpServerAsync();
@@ -1333,6 +1334,7 @@ public async Task DynamicClientRegistration_UsesExplicitApplicationType_WhenConf
                 },
             },
         }, HttpClient, LoggerFactory);
+#pragma warning restore MCPEXP001
 
         await using var client = await McpClient.CreateAsync(
             transport, loggerFactory: LoggerFactory, cancellationToken: TestContext.Current.CancellationToken);