Review of PR #356

[chalmerlowe]

Review Criteria & Output Format:

1. Conflict & Relevance Check:

• The PR applies cleanly without merge conflicts.
• It is highly relevant, addressing issue Flow.autogenerate_code_verifier does not default to True and flow.code_verifier is None #354 to enable PKCE by default, which is a security best practice.

2. Functional Correctness:

• The implementation aligns perfectly with the goal. autogenerate_code_verifier now defaults to True.
• The logic if self.code_verifier is None and self.autogenerate_code_verifier: in authorization_url is a crucial and correct addition. It ensures that if a user manually supplies a code_verifier (while autogenerate defaults to True), their manual value is respected and not overwritten. This handles the edge case of mixed configuration correctly.

3. Thoroughness:

• The change covers from_client_config, which also covers from_client_secrets_file.
• __init__ already had the correct default.
• The update propagates correctly to InstalledAppFlow.

4. Google Python Standards:

• Adherence is good.
• Docstrings are generally clear. The docstring for from_client_config implies kwargs are passed to OAuth2Session, but autogenerate_code_verifier is consumed. This is a pre-existing pattern for code_verifier as well, so it's acceptable, though a clarification in the docstring would be a "nit".
• Type hints (in docstrings) are consistent with the project style.

5. Technical Merit & Architecture:

• This is the right way to solve the problem. It enforces security by default while allowing opt-out (by passing autogenerate_code_verifier=False) or manual override (passing code_verifier).
• It is idiomatic and clean.

6. Testing:

• The tests in tests/unit/test_flow.py are well-updated.
• The addition of assert "code_challenge=" in url ensures the feature is active.
• The switch to re.fullmatch and stricter patterns for the verifier and challenge improves test rigor.
• All unit tests passed locally.

7. Critical Issues:

• None.
• This is a behavior change (enabling PKCE), but it is backward compatible with Google's OAuth 2.0 endpoints and improves security.

8. Suggested Refactors:

• None.

Verdict: LGTM

---

PR created automatically by Jules for task 8547016886391414059 started by @chalmerlowe

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.

[gemini-code-assist]

Summary of Changes

Hello @chalmerlowe, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the security posture of the google_auth_oauthlib library by making PKCE (Proof Key for Code Exchange) the default authentication flow. This change simplifies secure integration for developers by automatically handling the generation and management of code verifiers, while still allowing for manual override or explicit disabling. The accompanying test updates ensure the new default behavior is correctly validated and that the generated security parameters adhere to strict patterns.

Highlights

• Default PKCE Enablement: The autogenerate_code_verifier parameter in from_client_config now defaults to True, ensuring PKCE (Proof Key for Code Exchange) is enabled by default for new flows created from client configurations.
• Robust Code Verifier Handling: The logic in authorization_url was refined to only auto-generate a code_verifier if one is not already present (self.code_verifier is None), preventing accidental overwrites of manually provided verifiers even when auto-generation is enabled.
• Enhanced Test Coverage and Rigor: New assertions were added to test_authorization_url to explicitly check for code_challenge and code_challenge_method. Existing tests were made more robust by using re.fullmatch with precise length checks for code_verifier and code_challenge regex patterns, and mock.ANY for generated verifiers.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request correctly enables PKCE by default, which is a significant security improvement. The change is implemented by updating the default value for autogenerate_code_verifier in from_client_config and ensuring that a manually provided code_verifier is not overwritten. The tests have been updated thoroughly to cover the new default behavior and have been made more robust by using stricter regex matching. I've found one minor opportunity for improvement in the tests to reduce code duplication, which I've commented on. Overall, this is a solid and well-executed change.

[gemini-code-assist]

This regex for validating the code verifier is also used in test_authorization_url_generated_verifier. To improve maintainability and avoid duplication, consider extracting it into a module-level or class-level constant.

For example:

VALID_PKCE_VERIFIER_REGEX = r"^[A-Za-z0-9-._~]{128}$"

Then you could use this constant in both test methods.