fix: handle unregistered account on Google/social sign-in

[PavloNetrebchuk]

Problem

Signing in with Google (or another social provider) from the Sign In screen fails with a generic "Something went wrong" whenever the Google identity has no corresponding account on the platform.

Under the hood, the mobile token-exchange endpoint POST /oauth2/exchange_access_token/{provider}/ runs the social-auth pipeline with AUTH_ENTRY_LOGIN_API, which only signs in an already existing / linked account (associate-by-email). A first-time or unlinked social identity therefore returns:

{"error": "invalid_grant", "error_description": "access_token is not valid"}

even though the provider resolves the user's details. This matches the community report: Android app Google SSO invalid_grant.

Changes

1. SignInViewModel — distinguish EdxError.InvalidGrantException on social login and show a specific, actionable message instead of the generic error:

   This Google account is not linked with any OpenEdX account. Please register.

   This mirrors the iOS app and guides new users to the existing Register → Continue with Google flow, which creates and links the account. Other social-login failures still fall through to the generic error.

2. GoogleAuthHelper — fix the requested Google OAuth scope. It was a malformed, email-only string ("oauth2: …/userinfo.email", note the stray space) and is now:

   oauth2:openid https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/userinfo.profile
   

   aligning with the iOS/web clients and the server-side google-oauth2 DEFAULT_SCOPE (["openid", "email", "profile"]).

3. New string auth_social_account_not_registered.

Testing

Verified end-to-end on an emulator against a local Tutor Open edX with real Google OAuth clients:

• Unregistered Google account: Sign In → Google → exchange returns invalid_grant → the new "not linked… please register" message is shown (previously: generic error).
• Register → Continue with Google: the form is pre-filled with the Google name/email, registration 200 creates + links the account, the exchange then returns 200, and the user lands on the dashboard.
• Existing/linked account: Sign In → Google signs in directly (200).
• ./gradlew detektAll :auth:testDevelopDebugUnitTest passes.

[openedx-webhooks]

Thanks for the pull request, @PavloNetrebchuk!

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[volodymyr-chekyrta]

LGTM 👍