OAuth metadata url building should use authorization_server as base_url rather than mcp server url #762

Describe the bug
When I'm trying to connect to github-mcp-server, it always raises a 403 Error. After investigating code I believe it's due to wrong base_url when building authorization server url.

To Reproduce
Steps to reproduce the behavior:

1. Mcp Server url: https://api.githubcopilot.com/mcp
2. Protected Resource metadata:
   response from GitHub OAuth server:

{'resource_name': 'GitHub MCP Server',
 'resource': 'https://api.githubcopilot.com/mcp',
 'authorization_servers': ['https://github.com/login/oauth'],
 'bearer_methods_supported': ['header'],
 'scopes_supported': ['gist',
  'notifications',
  'public_repo',
  'repo',
  'repo:status',
  'repo_deployment',
  'user',
  'user:email',
  'user:follow',
  'read:gpg_key',
  'read:org']}

3. Try to get OAuth metadata
   Current code

    const metadata = await discoverOAuthMetadata(serverUrl, {
        authorizationServerUrl
    });

then the built metadata well-known url is /.well-known/oauth-authorization-server/mcp which path comes from mcp server url. However the right url should be /.well-known/oauth-authorization-server/login/oauth and the path comes from authorization_servers.

Expected behavior
Build the metadata url with authorization_servers.

Additional context
I also tried python sdk and it is working. the related code is using authorization_server_url to build the metadata url.