Auth: Add Google OAuth

[tianjing-li]

• Adds base Google OAuth logic
• Modifies existing /login and /auth endpoints to interface with these Auth strategies

Note: OAuth not in usable state after merging this, will require JWT token

TODO:

• Remove SessionMiddleware usage, replace with JWT token auth
• E2E testing with FE

[malexw]

There's nothing that really jumps out at me here, though it should probably get a review from someone who's more familiar with the backend than me.

[tianjing-li]

@EugeneLightsOn I've added this ticket: https://linear.app/cohereai/issue/EXT2-74/add-jwt-token-bearer-header-to-requests-remove-usage-of-session

To track the work of removing session and using a JWT token based auth

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 72.11538% with 29 lines in your changes are missing coverage. Please review.

Please upload report for BASE (main@f96ef06). Learn more about missing BASE report.

Files	Patch %	Lines
src/backend/routers/auth.py	51.61%	15 Missing ⚠️
src/backend/services/auth/google_oauth.py	75.00%	7 Missing ⚠️
src/backend/services/auth/utils.py	56.25%	7 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #138   +/-   ##
=======================================
  Coverage        ?   87.85%           
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  Files           ?      116           
  Lines           ?     3673           
  Branches        ?        0           
=======================================
  Hits            ?     3227           
  Misses          ?      446           
  Partials        ?        0           

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[malexw]

🚢 🇮🇹