fix(client-oauth2): 👻 ensure client_credentials flow follows RFC 6749

[yonathan9669]

Summary

This PR ensures that the OAuth2 client credentials flow strictly follows RFC 6749 specifications, particularly section 4.4.3, which states that no refresh token should be included in the response.

Changes Made

• Modified the ClientOAuth2Token class to handle the client credentials flow without expecting a refresh token
• Updated the credentials flow implementation to properly handle token responses according to the spec
• Added type safety to distinguish between different grant types

Testing

• Verified that client credentials flow works without refresh tokens
• Confirmed that token refresh attempts are made for client credentials grant type
• Ensured backward compatibility with existing implementations

Related Issues

• Fixes: OAuth2 Client Credentials | Not refreshing expired tokens
• Ref: OAUTH Bearer Token Refresh Issue?

Additional Context

According to RFC 6749 Section 4.4.3, the client credentials flow should not return a refresh token. This change ensures compliance with the specification while maintaining backward compatibility with existing code.

Note: I have touched the minimum amount of code to solve the issue and preserve current behavior. I assume a better solution could be set in place but this would cover both scenarios for now.

Review Checklist

• PR title and summary are descriptive
• Code follows project style guidelines
• Tests have been added/updated
• Documentation has been updated if needed

[CLAassistant]

All committers have signed the CLA.

[cubic-dev-ai]

cubic reviewed 4 files and found no issues. Review PR in cubic.dev.

[Joffcom]

Hey @yonathan9669,

Thanks for the PR, We have created "GHC-2537" as the internal reference to get this reviewed.

One of us will be in touch if there are any changes needed, in most cases this is normally within a couple of weeks but it depends on the current workload of the team.

[yonathan9669]

Hey @Joffcom, thanks for your quick reply.

Awesome, I hope this small fix can help others facing similar issues with OAuth2 client credentials. 🤝

I'll be available to improve anything if it's required. There might be opportunities for further improvements, but I wanted to start with the most straightforward fix for the immediate issue.

Thanks a lot in advance for accepting my contribution to this amazing community 🙏🏻