feat: add serialization for code challenge methods in metadata

[appleboy]

• Add support for serializing supported code challenge methods in AuthServerMetadata

Description

For https://datatracker.ietf.org/doc/html/rfc8414

code_challenge_methods_supported

OPTIONAL. JSON array containing a list of Proof Key for Code
Exchange (PKCE) [RFC7636] code challenge methods supported by this
authorization server. Code challenge method values are used in
the "code_challenge_method" parameter defined in Section 4.3 of
[RFC7636]. The valid code challenge method values are those
registered in the IANA "PKCE Code Challenge Methods" registry
[IANA.OAuth.Parameters]. If omitted, the authorization server
does not support PKCE.

	router.GET("/.well-known/oauth-authorization-server", corsMiddleware(), func(c *gin.Context) {
		metadata := transport.AuthServerMetadata{
			Issuer:                            "http://localhost:8080",
			AuthorizationEndpoint:             "https://github.com/login/oauth/authorize",
			TokenEndpoint:                     "https://github.com/login/oauth/access_token",
			RegistrationEndpoint:              "http://localhost:8080/register",
			ScopesSupported:                   []string{"openid", "profile", "email"},
			ResponseTypesSupported:            []string{"code"},
			GrantTypesSupported:               []string{"authorization_code", "client_credentials", "refresh_token"},
			TokenEndpointAuthMethodsSupported: []string{"none"},
			CodeChallengeMethodsSupported:     []string{"S256"},
		}
		c.JSON(http.StatusOK, metadata)
	})

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• MCP spec compatibility implementation
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring (no functional changes)
• Performance improvement
• Tests only (no functional changes)
• Other (please describe):

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• I have updated the documentation accordingly

MCP Spec Compliance

• This PR implements a feature defined in the MCP specification
• Link to relevant spec section: OAuth 2.0 Authorization Server Metadata
• Implementation follows the specification exactly

Summary by CodeRabbit

• New Features
  • Added support for displaying the code challenge methods supported by the OAuth authorization server.

[coderabbitai]

Walkthrough

The AuthServerMetadata struct in the OAuth client transport was extended by adding a new optional field CodeChallengeMethodsSupported to represent supported PKCE code challenge methods. No other code or logic changes were made.

Changes

File(s)	Change Summary
client/transport/oauth.go	Added CodeChallengeMethodsSupported []string field to AuthServerMetadata struct with JSON tag code_challenge_methods_supported

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (1.64.8)

Error: you are using a configuration file for golangci-lint v2 with golangci-lint v1: please use golangci-lint v2
Failed executing command with error: you are using a configuration file for golangci-lint v2 with golangci-lint v1: please use golangci-lint v2

---

📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 17982da and 2d62e3c.

📒 Files selected for processing (1)

• client/transport/oauth.go (1 hunks)

✅ Files skipped from review due to trivial changes (1)

• client/transport/oauth.go

✨ Finishing Touches

• 📝 Generate Docstrings

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

🪧 Tips

Chat

There are 3 ways to chat with CodeRabbit:

• Review comments: Directly reply to a review comment made by CodeRabbit. Example:
  • I pushed a fix in commit <commit_id>, please review it.
  • Explain this complex logic.
  • Open a follow-up GitHub issue for this discussion.
• Files and specific lines of code (under the "Files changed" tab): Tag @coderabbitai in a new review comment at the desired location with your query. Examples:
  • @coderabbitai explain this code block.
  • @coderabbitai modularize this function.
• PR comments: Tag @coderabbitai in a new PR comment to ask questions about the PR branch. For the best results, please provide a very specific query, as very limited context is provided in this mode. Examples:
  • @coderabbitai gather interesting stats about this repository and render them as a table. Additionally, render a pie chart showing the language distribution in the codebase.
  • @coderabbitai read src/utils.ts and explain its main purpose.
  • @coderabbitai read the files in the src/scheduler package and generate a class diagram using mermaid and a README in the markdown format.
  • @coderabbitai help me debug CodeRabbit configuration file.

Support

Need help? Create a ticket on our support page for assistance with any issues or questions.

Note: Be mindful of the bot's finite context window. It's strongly recommended to break down tasks such as reading entire modules into smaller chunks. For a focused discussion, use review comments to chat about specific files and their changes, instead of using the PR comments.

CodeRabbit Commands (Invoked using PR comments)

• @coderabbitai pause to pause the reviews on a PR.
• @coderabbitai resume to resume the paused reviews.
• @coderabbitai review to trigger an incremental review. This is useful when automatic reviews are disabled for the repository.
• @coderabbitai full review to do a full review from scratch and review all the files again.
• @coderabbitai summary to regenerate the summary of the PR.
• @coderabbitai generate docstrings to generate docstrings for this PR.
• @coderabbitai generate sequence diagram to generate a sequence diagram of the changes in this PR.
• @coderabbitai resolve resolve all the CodeRabbit review comments.
• @coderabbitai configuration to show the current CodeRabbit configuration for the repository.
• @coderabbitai help to get help.

Other keywords and placeholders

• Add @coderabbitai ignore anywhere in the PR description to prevent this PR from being reviewed.
• Add @coderabbitai summary to generate the high-level summary at a specific location in the PR description.
• Add @coderabbitai anywhere in the PR title to generate the title automatically.

CodeRabbit Configuration File (.coderabbit.yaml)

• You can programmatically configure CodeRabbit by adding a .coderabbit.yaml file to the root of your repository.
• Please see the configuration documentation for more information.
• If your editor has YAML language server enabled, you can add the path at the top of this file to enable auto-completion and validation: # yaml-language-server: $schema=https://coderabbit.ai/integrations/schema.v2.json

Documentation and Community

• Visit our Documentation for detailed information on how to use CodeRabbit.
• Join our Discord Community to get help, request features, and share feedback.
• Follow us on X/Twitter for updates and announcements.