How to create new nginx User from Website inputs?

I am trying to create a new nginx user on my Server with inputs from the Website. in alternativ to system(...) I also tried exec(...) and shell_exec(...). nothing seems to happen :/ i am very inexperienced sorry.

this command should be executed in linux "htpasswd /etc/nginx/.htpasswd (username)" then your prompted to put in a password and finally repeat that password.

<form action="make-user.php" method="get">
  Username: <input type="text" name="username">
  Password: <input type="password" name="password1">
  repeat Password: <input type="password" name="password2">
  <input type="submit">
</form>

<br>

<?php   $username = $_GET["username"]   ?>
<?php   $password1 = $_GET["password1"]  ?>
<?php   $password2 = $_GET["password2"]  ?>
<?php   system("htpasswd /etc/nginx/.htpasswd $username");   ?>
<?php   system("$password1");   ?>
<?php   system("$password2");   ?>