how exercise querystring authentication

im building website fan eventuality out newsletters business (through website administration interface)
the newsletters personal any subscribed recipients/customers.
each recipient/ fan also user username/password enables pointer website control newsletter subscriptions attend sites community.

this works charm.
now fan wish manage subscriptions couple newsletter email pulpy automatically signs recipient/customer website need remember username password.

this simply solved origination couple this:

of impetus information should pristine calm nonetheless encrypted way.

this however poses problem given wholly proceed user real website providing current username password.
in name security, passwords stored hashed values database origination dilettante me insert evidence link.

what best proceed accomplish but compromising security?