When Absolute Uri passed as McpAuthenticationOptions.ResourceMetadataUri, /.well-known/oauth-protected-resource endpoint returns 404

Describe the bug

When Absolute Uri passed as McpAuthenticationOptions.ResourceMetadataUri, /.well-known/oauth-protected-resource endpoint returns 404.

The logic for matching resource metadata endpoint is only limited to relative path, when an absolute path is passed in, the match fails and allows the resource metadata request to fall through the pipeline.

To Reproduce

1. Provide an absolute Uri as as McpAuthenticationOptions.ResourceMetadataUri when configuring AddMcp
2. Start the server
3. Hit the resource metadata endpoint

Reproduced in sample server, added

AddMcp(options =>
{
  // ... resource metadata object
  options.ResourceMetadataUri = new Uri($"{serverUrl}.well-known/oauth-protected-resource", UriKind.Absolute);
}

in samples\ProtectedMCPServer\Program.cs

Expected behavior
Resource metadata request should be handled when provided a valid ResourceMetadataUri

Unit tests failure when configure the absolute uri

Start with samples\ProtectedMCPServer\Program.cs and reproduce the request using an absolute ResourceMetadataUri configured through AddMcp. Then locate the resource metadata endpoint matching logic and the unit tests referenced by the issue. Done means a valid absolute URI is handled by the /.well-known/oauth-protected-resource endpoint instead of returning 404, with the relevant tests passing.