How to check if password exists?

Need help
3

Facebook works the same way (you can check if a user has a Facebook ID or Facebook email). I have 3 types of users

  1. User signs up with email
  2. User signs up with email, then connects their facbook account
  3. User signs up with facebook

I want to make sure 1) and 2) see the password change option, but 3) does not.