[squid-users] proxy_auth not working in squid

hi
   i m trying to use an external autentication program for squid i did downloaded mysql_auth.c and compiled it properly.now i changed settings like this

acl auth_user proxy_auth REQUIRED
authenticate_program <path to mysql_auth>

i dont know how it should work but i think that it should give a login prompt at client(browser as we get for htaccess)but its not working like this.
can any one tell me how to make it work

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Manish Kumar Arya