sorry for this stupid question. I have been looking up in google "where does apex get user details from for login in" and nothing answers my question. Basically I wanted to know when you log in your application how does apex know you have access to this application. How does it know you are a valid user because I am creating an application which basically checks if a user exist in one database and also checks if he/she exist in the second database.
Thanks you and sorry if this is very newbie