How to add user, authorize in firebase using php?

Question

PHP

I do not quite understand how authorization occurs, adding a user to firebase. I understand how to add something to the database, but I don’t understand how to add a user to Authentication.
Login method - Email address/password.
To access the database I use - kreait/firebase-php . It has documentation, but I also get lost in it.
If anyone has experience with this service, please tell the teapot :)