ClientOAuthProvider does not work with MS Entra

[eduardomb-aw]

Describe the bug
The current implementation of ClientOAuthProvider is not compatible with MS Entra directories. Both the RefreshTokenAsync and ExchangeCodeForTokenAsync methods make use of a "resource" parameter that does not work in Entra; Entra uses "scope".

To Reproduce
Steps to reproduce the behavior:

1. Replace the InMemoryOAuthServer information used in the samples ProtectedMcpServer and ProtectedMcpClient with a real MS Entra directory info (including the proper app registrations, secrets, and permissions), and run the sample. The ClientOAuthProvider will throw and exception:

Expected behavior
The implementation should ALSO work with MS Entra.

Logs

Authorization code received successfully from Microsoft Entra ID.
fail: ModelContextProtocol.Client.McpClient[1155727496]
      Client (ProtectedMcpClient 1.0.0.0) client initialization error.
      System.Net.Http.HttpRequestException: Response status code does not indicate success: 400 (Bad Request).
         at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
         at ModelContextProtocol.Authentication.ClientOAuthProvider.FetchTokenAsync(HttpRequestMessage request, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Authentication\ClientOAuthProvider.cs:line 409
         at ModelContextProtocol.Authentication.ClientOAuthProvider.ExchangeCodeForTokenAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, String authorizationCode, String codeVerifier, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Authentication\ClientOAuthProvider.cs:line 403
         at ModelContextProtocol.Authentication.ClientOAuthProvider.InitiateAuthorizationCodeFlowAsync(ProtectedResourceMetadata protectedResourceMetadata, AuthorizationServerMetadata authServerMetadata, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Authentication\ClientOAuthProvider.cs:line 336
         at ModelContextProtocol.Authentication.ClientOAuthProvider.PerformOAuthAuthorizationAsync(HttpResponseMessage response, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Authentication\ClientOAuthProvider.cs:line 233
         at ModelContextProtocol.Authentication.ClientOAuthProvider.HandleUnauthorizedResponseAsync(String scheme, HttpResponseMessage response, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Authentication\ClientOAuthProvider.cs:line 183
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.HandleUnauthorizedResponseAsync(HttpRequestMessage originalRequest, JsonRpcMessage originalJsonRpcMessage, HttpResponseMessage response, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Authentication\AuthenticatingMcpHttpClient.cs:line 68
         at ModelContextProtocol.Authentication.AuthenticatingMcpHttpClient.SendAsync(HttpRequestMessage request, JsonRpcMessage message, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Authentication\AuthenticatingMcpHttpClient.cs:line 30
         at ModelContextProtocol.Client.StreamableHttpClientSessionTransport.SendHttpRequestAsync(JsonRpcMessage message, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Client\StreamableHttpClientSessionTransport.cs:line 76
         at ModelContextProtocol.Client.AutoDetectingClientSessionTransport.InitializeAsync(JsonRpcMessage message, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Client\AutoDetectingClientSessionTransport.cs:line 69
         at ModelContextProtocol.Client.AutoDetectingClientSessionTransport.InitializeAsync(JsonRpcMessage message, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Client\AutoDetectingClientSessionTransport.cs:line 90
         at ModelContextProtocol.McpSessionHandler.SendRequestAsync(JsonRpcRequest request, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\McpSessionHandler.cs:line 440
         at ModelContextProtocol.McpSession.SendRequestAsync[TParameters,TResult](String method, TParameters parameters, JsonTypeInfo`1 parametersTypeInfo, JsonTypeInfo`1 resultTypeInfo, RequestId requestId, CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\McpSession.Methods.cs:line 71
         at ModelContextProtocol.Client.McpClientImpl.ConnectAsync(CancellationToken cancellationToken) in C:\Temp\repos\mcp-csharp-sdk\src\ModelContextProtocol.Core\Client\McpClientImpl.cs:line 150
info: ModelContextProtocol.Client.McpClient[2103773711]
      Secure Weather Client message processing canceled.

Additional context
Add any other context about the problem here.