The former is always true (outside of post method it is an empty array
and not null, and it cannot be `unset()`).
The check was as such either meaningless or was supposed to check that
something was sent. This commit assume the later.
Now use passwords hashed & salted. Validate with PHP's password_verify() function
Password hashes can be generated with :
* mkpasswd --method=sha-512
* PHP's password_hash()