Add UserAccessValidator to enforce per-user access in REST API

[Kenasvarghese]

This PR introduces a UserAccessValidator interface to the ADK REST API, enabling per-user access control for sessions, runtime, and artifacts endpoints.

Changes include:

• Added UserAccessValidator interface and UserAccessValidatorFunc adapter.
• Updated API controllers (Sessions, Runtime, Artifacts) to use the validator before performing operations.
• Updated handler and launcher to pass the validator.
• Added test cases for unauthorized access scenarios.

By default, existing behavior is unchanged if no validator is provided.

This allows applications to enforce custom authorization rules for API endpoints.

Related Issues:

• Fixes user_id parameter validation in session endpoints #507

[gemini-code-assist]

Summary of Changes

Hello @Kenasvarghese, 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 ADK REST API's security and extensibility by introducing a pluggable user access validation mechanism. It allows applications to define and enforce custom authorization rules for specific API endpoints related to sessions, runtime operations, and artifacts. This change provides a robust framework for implementing fine-grained access control, making the API more secure and adaptable to diverse authorization requirements without altering core API logic.

Highlights

• Introduced UserAccessValidator Interface: A new UserAccessValidator interface and UserAccessValidatorFunc adapter have been added, providing a flexible mechanism for defining custom per-user access control logic.
• Integrated Validator into API Controllers: The Sessions, Runtime, and Artifacts API controllers now utilize the UserAccessValidator to enforce authorization checks before processing requests, ensuring secure access to resources.
• Updated API Handler and Launcher: The main API handler (adkrest.NewHandler) and the API launcher (api.go) have been updated to accept and propagate the UserAccessValidator instance throughout the API setup.
• Enhanced Test Coverage for Access Control: New test cases have been added to sessions_test.go to specifically cover scenarios involving unauthorized access, validating the correct behavior of the new access control logic.
• Backward Compatibility Maintained: The UserAccessValidator is optional; if no validator is provided, the API maintains its existing behavior, ensuring backward compatibility for current applications.

🧠 New Feature in Public Preview: You can now enable Memory to help Gemini Code Assist learn from your team's feedback. This makes future code reviews more consistent and personalized to your project's style. Click here to enable Memory in your admin console.

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 introduces a UserAccessValidator to enforce per-user access control in the REST API, which is a great enhancement for security and multi-tenancy. The implementation is clean, with the new validation logic correctly integrated into the API controllers for sessions, runtime, and artifacts. The addition of test cases for unauthorized access scenarios is also well done.

My review focuses on a few areas for improvement, mainly around code duplication in the controllers where the validation logic is called. Extracting this repeated code into helper methods would improve maintainability. I've also noted some minor inconsistencies in error handling and testing that could be aligned for better code quality.

[Kenasvarghese]

Please Review @yarolegovich @dpasiukevich