Using WP to authenticate

I need to know if I can use WP to authenticate users and then forward them on to another website via a link WP would create on the fly that includes a MD5 hash of several variables. Does anyone know of an easy way to accomplish this? How about a plugin that might work? The MD5 has would be emailaddress+todaysdate+none+secretpasscode

Can anyone help? I apologize if this should be posted elsewhere. Thanks!