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Accept HTTP Basic client authentication at the token endpoint - #13
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The token endpoint only read client_id and client_secret from the request body, and the server metadata did not list token_endpoint_auth_methods_supported. Clients then default to client_secret_basic (RFC 8414), which this server rejected with invalid_client. RubyLLM 2.1 does exactly that, so connecting from the AI platform failed. Accept HTTP Basic credentials (RFC 6749 section 2.3.1) alongside the request body, and advertise both methods. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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🟡 Changes recommended
Malformed credentials can cause a 500, and Basic authentication failures omit the required challenge header.
4 open findings
What changed in this PR
Adds HTTP Basic client authentication support to the OAuth token endpoint.
Changes:
- Advertises Basic and POST client authentication methods.
- Parses form-encoded Basic credentials.
- Adds authentication and metadata specs.
| File | Description |
|---|---|
lib/mail_mcp/app.rb |
Implements and advertises Basic authentication. |
spec/mail_mcp/app_spec.rb |
Tests Basic authentication and discovery metadata. |
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| auth = Rack::Auth::Basic::Request.new(request.env) | ||
| return [params[:client_id], params[:client_secret]] unless auth.provided? && auth.basic? |
| auth = Rack::Auth::Basic::Request.new(request.env) | ||
| return [params[:client_id], params[:client_secret]] unless auth.provided? && auth.basic? | ||
|
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| auth.credentials.map { |part| URI.decode_www_form_component(part) } |
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| it "accepts client credentials sent with HTTP Basic authentication" do | ||
| basic_authorize URI.encode_www_form_component(client_id), URI.encode_www_form_component(client_secret) |
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| redirect_uri: redirect_uri, | ||
| client_id: client_id |
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Problem
POST /oauth/tokenreadclient_idandclient_secretonly from the request body, and/.well-known/oauth-authorization-serverdidn't listtoken_endpoint_auth_methods_supported. Without that field, clients default toclient_secret_basic(RFC 8414) and send the credentials in anAuthorization: Basicheader. The server then saw an empty secret and answered401 invalid_client.RubyLLM 2.1 follows that default, so connecting the Mail connector from the AI platform fails with "Failed to complete OAuth authorization". The older
ruby_llm-mcpgem sent the secret in the body, which is why it worked before.Fix
token_endpoint_auth_methods_supported: ["client_secret_basic", "client_secret_post"].Tests
bundle exec rspec(Ruby 3.4.9): 86 examples, 0 failures. RuboCop: no offenses in the changed files.After merging, this needs a release (1.0.4) and a bump of
mcp/mail/Gemfilein the AI platform.🤖 Generated with Claude Code