Without a secure server, the best you can probably do is use the crypt(); function to encrypt the password. Have an encryption for a password stored in a file with permissions set as strictly as possible. Keep in mind, the login and password are still being sent through the wires unencrypted though. That is the cost of an unsecure server.

#don't name it $password in real life!
my $crypted = $crypt($password, $key);
open (PASSWORD, ".somefile") or die "login failed";
if ($crypted eq <PASSWORD>)
   { let them in }
else { don't let them in }
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This code is untested and for example purposes only.