Attach OAuth2 login to existing users in a Spring Boot application
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