feat: add Google OAuth authentication support

[izyuumi]

• Implement Google OAuth authorization flow
• Add callback server for handling OAuth responses
• Integrate Google authentication into CLI commands
• Enable access token management for Google users

[izyuumi]

Any ideas as to how I can fix this AI_APICallError: Request had insufficient authentication scopes. error?

[izyuumi]

This PR would fix #402

[ZeroIDdev]

check the cline implementation of gemini cli as provider

[izyuumi]

Thank you for the advice. I'll note this here for myself: cline/cline#4472

[Gibgoyt]

Is this PR something similar to what Gemini CLI has when we log in with our Google Account and then still have free access to Gemini 2.5 Pro models? Or is it still like the API where there is only a free tier on the 2.5 flash only??

[izyuumi]

@Gibgoyt The former, where it's like Google CLI free access to Gemini 2.5 Pro!

[izyuumi]

I now need a GOOGLE_CLOUD_PROJECT or something similar (here). Does anyone have any idea where I could find the one used for Gemini CLI (is it even allowed to used that?)? Below is the error I am getting atm.

[SachinJadeja]

@izyuumi I dont think you can get one used in google cli but since its only OAuth, someone could create the Oauth credentials and put it under the env vars. Probably @thdxr could help here(for the credentials).

[izyuumi]

Thanks for the info. If you could help, it'd be really appreciated @thdxr

[Gibgoyt]

Yo, I cloned, added my Google Auth 2 client key and secret
I cloned your git commit

I am assuming that's all I need to do? I logged in fine, but can't get responses from Gemini, some API error

[thdxr]

https://x.com/cline/status/1939129177807913024

i'm still planning on making a plugin system and people can load their own plugins but we can't support this officially

[izyuumi]

Makes sense 😭

[aspiers]

@thdxr Please see cline/cline#4495 - unless I'm misunderstanding, it looks like the Gemini CLI maintainer isn't against other agents routing requests through their offering as long as it's done in the right way. Seems that he's already collaborating with the Cline team to get this done, so maybe opencode can launch a similar collab?