Authentication is the process to detect who the user is. On the other hand Authorization is the process to decide what kind of information a user can access.
As an Example:
Create an account with some document is Authentication. These documents can be phone number, email address, nid number and so on...
Again, accessing that account information in other times with password and other info. is Authentication.
I use firebase, because firebase is simple, lightweight, beginners friendly and industrially recognized.
We can use other options instead of firebase. They are...
Besides authentication firebase offers a number of services. They are