Claude Code MCP authentication fails: OAuth 404 and API key 'unauthorized'

[minac]

Environment

• Client: Claude Code CLI (latest)
• OS: macOS Darwin 25.1.0
• MCP URL: https://mcp.render.com/mcp

Problem

When configuring the Render MCP server in Claude Code, authentication fails in two different scenarios:

Scenario 1: With API Key Header

Config:

{
  "render": {
    "type": "http",
    "url": "https://mcp.render.com/mcp",
    "headers": {
      "Authorization": "Bearer <VALID_API_KEY>"
    }
  }
}

• Claude Code shows: Auth: ✗ not authenticated
• MCP tools like list_services return unauthorized
• However, select_workspace and get_selected_workspace work correctly
• The same API key works perfectly with the REST API (api.render.com/v1/services)

Scenario 2: Without API Key (OAuth flow)

When removing the Authorization header and clicking "Authenticate" in Claude Code:

Error: HTTP 404: Invalid OAuth error response: SyntaxError: JSON Parse error: Unable to parse JSON string. Raw body: 404 page not found

The OAuth endpoint appears to return a 404.

Expected Behavior

Either:

1. API key authentication should work as documented
2. OAuth flow should open browser and complete authentication

Steps to Reproduce

1. Add Render MCP server to Claude Code: claude mcp add --transport http render https://mcp.render.com/mcp --header "Authorization: Bearer <API_KEY>"
2. Run /mcp in Claude Code
3. Observe "Auth: ✗ not authenticated"
4. Try using any tool like list_services → returns "unauthorized"
5. Alternatively, remove the header and click "Authenticate" → 404 error

Workaround

Using the REST API directly works fine with the same API key.

[yannbc]

Also experiencing this issue when using the MCP server from Tasklet.ai. API key auth returns 'unauthorized' for most tools (list_services, list_workspaces, etc.), though select_workspace and get_selected_workspace do work. The same API key works perfectly with the REST API at api.render.com.