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 someone@gmail.com
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