How does session management work with firebase-auth-serverless?

[vedantroy]

In the serverless firebase auth example, there is an instruction to store the authentication token with something like express-session. However, express-session would only make sense in a scenario where there is a server, right? Not in a serverless environment.

I suppose we can use an external store, like connect-dynamodb, but, won't that mean every lambda will have to import code to query the external database?

https://github.com/zeit/next.js/blob/9baa103bb81ef0b6dceb6ccc78a772dda251e309/examples/with-firebase-authentication-serverless/pages/api/login.js#L12