use Digest::SHA qw(sha256_hex);
my $password = $cgi->param('Passwort');
my $hashed = sha256_hex($password);

my $user = $cgi->param('Benutzername');

my $sth = $dbh->prepare("SELECT UserId FROM logins WHERE User = ? AND Passwordhash = ?"); 
$sth->execute($user,$hashed);