Third Party Login

If a non-logged in user authenticates with a third party through your OAuth flow, there are three possible outcomes:

The provider account they authenticated with is already connected with an account in your app, in which case you can log them in to that account.
The provider account they authenticated with is not connected with an account in your app, but the email address they authenticated with matches the email address of an account in your app, in which case you can connect the provider account with that account and log them in.
The provider account they authenticated with is not connected with an account in your app and doesn't match an email address in your app, in which case you can send them to onboarding.

In this exercise, we're going to handle scenario 1 and 3. We'll get to scenario 2 in the next exercise.

For the login scenario, we want to reuse a lot of logic from our regular login flow as far as creating a session and sending the user to enter their 2FA code if they haven't done that yet.

For the onboarding scenario, we need to be more thoughtful about the user experience. One of the nice things about connecting with a third party account is we have an opportunity to pre-fill a bunch of profile information for the new account based on what we get back from the provider.

So you're going to be doing that in this exercise! Have a good time!