Facebook, Apple, Google don’t know your password. They just don’t store it in their databases so hackers can’t retrieve it in case they manage to break in. But if you’re the only person who actually knows your password how do they know you are typing the right password to let you in? Great tip: If the web service you use would email you your passwordmeaning that they actually store itbetter run away from them. I love his presentation and the stuff he talks about on Computerphile.”]
Source: https://gizmodo.com/facebook-doesnt-know-your-password-so-how-does-it-know-1616900918