[Visual Studio] cannot connect to remote MCP server `"Invalid content type: must be 'application/json'\n"`

[xperiandri]

Describe the bug

I've put such configuration to .mcp.json

{
  "servers": {
    "GitHub": {
      "type": "http",
      "url": "https://api.githubcopilot.com/mcp/",
      "headers": {
        "Authorization": "Bearer ${input:github_pat}"
      }
    }
  },
  "inputs": [
    {
      "id": "github_pat",
      "description": "GitHub personal access token",
      "type": "promptString",
      "password": true
    }
  ]
}

and got in Copilot output

[NextEditSuggestionsService Information] 0 next edit suggestions available
[Conversations Information] [Conversations] Found 2 MCP server(s) defined in "C:\Users\Andrii\Dev\GitHub\FSharp.Collections.Immutable\.mcp.json": Microsoft Docs, GitHub
[Conversations Information] [Conversations] Found 2 MCP server(s) defined in "C:\Users\Andrii\Dev\GitHub\FSharp.Collections.Immutable\.mcp.json": Microsoft Docs, GitHub
[Conversations Error] [Conversations] Failure while initializing MCP server 'GitHub'. System.Net.Http.HttpRequestException: Response status code does not indicate success: 400 (Bad Request).
   at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
   at ModelContextProtocol.Client.StreamableHttpClientSessionTransport.SendMessageAsync(JsonRpcMessage message, CancellationToken cancellationToken)
   at ModelContextProtocol.McpSession.SendRequestAsync(JsonRpcRequest request, CancellationToken cancellationToken)
   at ModelContextProtocol.McpEndpointExtensions.SendRequestAsync[TParameters,TResult](IMcpEndpoint endpoint, String method, TParameters parameters, JsonTypeInfo`1 parametersTypeInfo, JsonTypeInfo`1 resultTypeInfo, RequestId requestId, CancellationToken cancellationToken)
   at ModelContextProtocol.Client.McpClient.ConnectAsync(CancellationToken cancellationToken)
   at ModelContextProtocol.Client.McpClient.ConnectAsync(CancellationToken cancellationToken)
   at ModelContextProtocol.Client.McpClientFactory.CreateAsync(IClientTransport clientTransport, McpClientOptions clientOptions, ILoggerFactory loggerFactory, CancellationToken cancellationToken)
   at ModelContextProtocol.Client.McpClientFactory.CreateAsync(IClientTransport clientTransport, McpClientOptions clientOptions, ILoggerFactory loggerFactory, CancellationToken cancellationToken)
   at Microsoft.VisualStudio.Conversations.Service.Mcp.McpServerTracker.<>c__DisplayClass8_0.<<-ctor>b__0>d.MoveNext() in D:\a\_work\1\s\src\Copilot.Service\Mcp\McpServerTracker.cs:line 60

Then I attached to Visual Studio, debugged ModelContextProtocol.Client.StreamableHttpClientSessionTransport class and saw that response is "Invalid content type: must be 'application/json'\n"

Affected version

I don't know, I use the remote one
Visual Studio 2022 Version 17.14.5 Preview 1.0

Steps to reproduce the behavior

1. Open solution
2. Create .mcp.json with the content above
3. Save
4. See error in Copilot output

Expected vs actual behavior

Visual Studio successfully gets the MCP tools list

[SamMorrowDrums]

It is probably sending application/json; charset=utf-8

We will address this in Monday (I think we will strip the additional part of the headers).

The headers sent are not necessarily valid for MCP as they add the character set extension and the MCP specification itself says exactly this:

The client **MUST** include an `Accept` header, listing both `application/json` and
   `text/event-stream` as supported content types.

Which is perhaps being applied too strictly. We are looking into it.