feat : add Google Calendar backend OAuth2 routes

[tmdeveloper007]

Summary of What Needs to be Done

The Interview Prep frontend defines GOOGLE_CALENDAR API paths in frontend/src/utils/apiPaths.js (CONNECT, CALLBACK, STATUS, EVENTS), but the backend has no mounted /api/google-calendar/* routes. Every calendar action always fails with a 404.

Changes that Need to be Made

1. Create backend/routes/googleCalendarRoutes.js with routes for:
   • GET /connect — initiate Google OAuth2 flow (stub or real)
   • GET /callback — handle OAuth2 callback
   • GET /status — check if user has connected calendar
   • POST /events — sync/save events
2. Mount the router in backend/server.js.
3. Add appropriate environment variable placeholders.

Impact that it would Provide

Makes the Google Calendar connect/sync UI functional instead of always failing with 404 errors. Provides a foundation for real OAuth2 integration.

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[dpi26]

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[dpi26]

Add Google Calendar Backend Routes

Summary

This PR adds the missing backend routes required by the Interview Prep frontend for Google Calendar integration.

The frontend already defines the following Google Calendar API paths in frontend/src/utils/apiPaths.js, but the backend did not have a corresponding mounted router. As a result, all Google Calendar actions were returning 404 Not Found.

Changes Made

• Added backend/routes/googleCalendarRoutes.js.

• Added the following Google Calendar endpoints:

  • GET /api/google-calendar/connect
  • GET /api/google-calendar/callback
  • GET /api/google-calendar/status
  • POST /api/google-calendar/events

• Mounted the Google Calendar router in backend/server.js.

• Added Google Calendar OAuth environment variable placeholders to backend/.env.example.

• Kept the implementation lightweight and prepared for future Google OAuth2/token persistence.

• Avoided changes to the existing MongoDB configuration because MongoDB is outside the scope of this issue.

API Behavior

GET /api/google-calendar/connect

Provides the entry point for initiating the Google Calendar OAuth flow.

GET /api/google-calendar/callback

Provides the callback endpoint required for Google OAuth integration.

GET /api/google-calendar/status

Returns the current calendar connection status.

Example response:

{
  "success": true,
  "connected": false
}

POST /api/google-calendar/events

Accepts calendar event data for synchronization/saving.

Example request:

{
  "events": [
    {
      "title": "Mock Interview",
      "start": "2026-08-25T10:00:00",
      "end": "2026-08-25T11:00:00"
    }
  ]
}

Environment Variables

Added placeholders for:

GOOGLE_CLIENT_ID=your_google_client_id
GOOGLE_CLIENT_SECRET=your_google_client_secret
GOOGLE_REDIRECT_URI=http://localhost:5000/api/google-calendar/callback

Actual credentials are not included in the repository.

Testing

Verified the backend Google Calendar endpoints locally:

• GET /api/google-calendar/connect
• GET /api/google-calendar/callback
• GET /api/google-calendar/status
• POST /api/google-calendar/events

The routes are now available instead of returning 404 Not Found.

Scope

This PR focuses specifically on the missing Google Calendar API routes and backend integration.

Full Google OAuth token persistence and production calendar synchronization can be implemented as a follow-up enhancement.

Issue

Closes #1927