feat(auth): add service-to-service authentication sample

[amcolin]

Description

Fixes Internal b/242962361

Checklist

• Tests pass
• Lint pass: bundle exec rubocop
• Please merge this PR for me once it is approved.

[gemini-code-assist]

Code Review

This pull request introduces a Ruby sample for service-to-service authentication using Cloud Functions, adding a Gemfile, a basic HTTP application, a helper to make authenticated GET requests, and integration tests. Feedback highlights critical issues in the implementation: the relay function in app.rb is hardcoded to return success instead of calling the target function, and the deployment script in service_auth_spec.rb uses the wrong entry point for the target function and fails to pass the target URL environment variable to the relay function. Additionally, improvements are recommended in service_auth.rb to validate the presence of the ID token and to configure connection and read timeouts on HTTP requests.

[XrossFox]

Not versed in ruby, but LG-enough-TM

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• auth/service-to-service/service_auth.rb:15, tag cloudrun_service_to_service_auth

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