A fitness club system verifies a scanned card against a database to check membership status;...

In the AAA model, Authentication is the act of proving identity and verifying that the account is valid and active. Just as the club system checks the database to confirm the cardholder is a legitimate member before opening the door, ClearPass checks an identity store (like AD or the Guest DB) to confirm a user's credentials are correct and their account hasn't expired before allowing them onto the network.