Connect a user's mailbox with Nylas hosted OAuth

Every Nylas request you make on a user's behalf needs one thing first: their permission. Before you can list a mailbox, send on someone's behalf, or read a calendar, the user has to authorize your application through their provider, and that authorization is what's called a grant. Doing the OAuth dance yourself means registering with Google and Microsoft separately, handling each provider's consent screen, token exchange, and refresh quirks. Hosted OAuth collapses that into one flow that works the same across every provider. This post walks through connecting an account from two angles: the HTTP API your web app uses in production, and the nylas CLI for connecting a test account from the terminal. I work on the CLI, so the terminal commands below are the ones I reach for when I need a grant to develop against. What a grant is A grant is an authenticated connection to a single user's account. When a user authorizes your application, Nylas stores the connection and hands you a grant_id , a stable identifier you pass on every subsequent request to act on that user's email, calendar, or contacts. The grant is the unit of access: one user who connected one mailbox is one grant, and everything you build addresses /v3/grants/{grant_id}/... . Keep two credentials distinct here. Your API key authenticates your application to Nylas and goes in the Authorization header on every request; the grant_id identifies which connected user that request acts on. The API key is yours and stays on your backend, while a grant_id is minted per user when they connect. The grant is also where provider differences disappear. A Gmail grant and a Microsoft grant have different OAuth scopes and token mechanics underneath, but once connected, both are just a grant_id you use the same way. That's the point of hosted OAuth: you run one flow, the user picks their provider, and you get back the same kind of identifier regardless of who hosts the mailbox. Hosted OAuth supports Google, Microsoft, Yahoo,