Castellum Authentication via Google

Allow users to sign up and sign in to Castellum using their Google account.

It verifies a Google ID token to create a Castelllum account with the respective email address as username.

p.s. the Google ID token verification is done on server side.

IMPORTANT: Google email address as Castellum username

It assumes your Castellum app is expecting to have email as username, otherwise your users might end up with two different accounts. e.g. 1st account with username someone and another account with username [email protected] because they are just usernames, but they are different, even though they are possibly the same user.

Meaning, if you need to look for users already registered with a different username, but same email address, you need to implement your own solution.

IMPORTANT: Google ID token as Castellum session

As long as a Google ID token is valid, it can work as a Castellum session, because the respective Castellum account can be retrieved from the ID token, as the Google email address in the ID token matches the username of the respective Castellum account.

How it works

sequenceDiagram
    autonumber
    Browser->>Google: Sign in with Google
    Google->>Browser: Google ID token
    Browser->>Castellum: Sign up with Google
    Castellum->>Google: Verify token
    Google->>Castellum: Token is valid
    Castellum->>Castellum: Create account
    Note right of Castellum: email address = username
    Castellum->>Castellum: Activate account
    Castellum->>Browser: Castellum account ID