Implement JavaScript validation on Register, Login, and Profile $($include $"[$Client$]"$ in the output messages to differentiate between server$-$side validations$).$ You just have to implement a validation on login$.$php$,$ that check to see if username or password and anything meets requirement or not. If it doesnt then send the client error message.

First $4$ images are my code for Login.php$.$ The fifth image is the code to disable the html validation to check if client side is work, you just input it into the console log in dev tools.