Google Calendar, API, & Gmail Integrations

I need our existing SaaS booking manager to tap directly into Google’s ecosystem so every customer who signs up can:

• connect their Google Calendar, see real-time availability inside our scheduler, and let us push confirmed bookings back to their calendar;
• send, receive, and log email through Gmail without ever leaving our app;
• rely on a clean, well-documented custom API layer that we can extend to other Google services later.

The sign-in step is already handled; what’s missing is the deep, token-based access to Calendar, Gmail, and any other Google endpoints we decide to expose. Your job is to build those flows end-to-end, handle refresh-token management, and return the data in a format our front-end can consume (React + Next.js). Our back-end runs on Node (Nest.js) with PostgreSQL, so familiarity there is helpful.

Please architect with scalability in mind, follow Google’s OAuth 2.0 best practices, and produce clear developer documentation (setup, scopes requested, sample requests, error handling). Experience with email servers, DKIM/SPF, and webhooks will give you an edge because we plan to roll out a custom mail relay next.

Once this phase ships smoothly, I’ll have follow-on work around expanding to additional Google APIs and possibly Microsoft 365.