SaaS invites and other logins

So, I am writing a SaaS and users are invited by the app via email and it is username and password. How then can I associate their Facebook/Google/Apple login with the user account?

Unsure of where to even start.
Richard

Question: When the users are invited are accounts created for them?

If so, you’re going to want to either handle invites in another way or provide a temporary password, then when they log in redirect them to a page to log in with a social network.

Yes, I create the users and send them a temporary password in the email.

Awesome! So when they log in redirect them to sign in with a social network.

using the “Signup/Login with a social network” workflow? Is that where the association happens?

Yes, exactly

Thank you very much!