Install mod_ssl on your Apache webserver. Configure the directory that your script is in to use SSL with the SSLRequireSSL directive. Here is a sample block from my server:

<Directory "/var/www/perl">
    Options FollowSymLinks
    AllowOverride All
    SSLRequireSSL
    Order allow,deny
    Allow from all
    AuthType Basic
    AuthName "Sample encrypted stuff"
    AuthUserFile conf/users
    Require valid-user
</Directory>
[download]

As you can see, I'm using basic (plaintext) authentication using the htpasswd utility and password file. Hope this helps.

-fp