We are planning to use social logins (like facebook, google, twitter, pinterest, and so on) in our app.
What are the rules for storing the facebook IDs (or google, twitter, ...) in our database? Do we need to hash it like passwords? What about the authentication tokens?
If a user deletes the app, can we contact him through his profile page to ask him why he deleted it? (assuming we are allowed to store the ID unhashed)
Clarification:
If the app is only deleted, the user ID would be stored for future logins from other devices. If the user wants to delete their account on our server, it would be deleted completely.