User authentication process.

Have you ever asked yourself how the user authentication process works?
Let's jump.

What is User Authentication?

User authentication is a security process that covers all of the human-to-computer interactions that require the user to register and log in.
Simply said, authentication asks each user: 'who the hell are you?'
and verifies their response.

Each user account contains two Unique Identifiers: Username and user identifier also abbreviated to user ID or UID.
When a user account is created, its Username is mapped to a unique UID.

Username is used to access the user account.
Username is also known as the login name.
UID is used to authenticate, track and monitor the activity of a user account. Username is used by the user while the UID is used by the system.

That unique ID and key will allow the user to access his/her account.

Process

When a user enters his/her username and password, depending on the type of user management model used, the following steps are performed in a local/ remote system.

1- The System checks whether the user account exists or not.

2- If the user account exists, it checks whether the user is allowed to login from that particular location where username and password are entered or not.

3- If the user is allowed to log in, it checks the supplied password.

4- If the supplied password is incorrect, it checks the threshold value for retries.

5- If the threshold value is exceeded, it locks the account.

6- If the threshold value is not exceeded, it allows the user to retype the correct password.

7- If the supplied password is correct, it checks the password expiry date.

8- If the password is expired, it forces the user to update his/her password.

9- If the password is about to expire, it shows a configured warning message which prompts the user to change his/her password before the expiry date.

10- If the supplied username and password are correct and all the above conditions are satisfied, the user is allowed to log in.

...with this, we end this tutorial on what a User authentication process in Linux is.
Cheers :~)