问题
I have a Spring Boot application that is "invitation only". Ie. users are sent a signup link and there is no "Sign up" functionality. This works fine and users log on with their username and password.
I would like to allow logon with FaceBook and Google using OAuth2 as a supplementary logon method. This would involve mapping the existing users to their social account in some way. The users and their passwords are stored in a MySQL database. I have found a number of articles on OAuth2 and Spring Boot, but none that address this exact use-case.
I can create the Google OAuth2 token/client secret etc, but how do I design the flow to allow only the existing users to logon with their social accounts?
The usernames have been chosen by the users themselves, and are therefore not necessarily the same as their email.
Do I need to create a custom authentication flow in this case? And do I need to change the authentication mechanism from cookies to JWT tokens?
来源：https://stackoverflow.com/questions/59224564/attach-oauth2-login-to-existing-users-in-a-spring-boot-application