Validate User ID one site to another site access.

Hi Frnds.

I am developing mobile site for desktop version web site,, here i have a problem i have download link in mobile site when user click download then ask user name. Pwd for validation if user is exist then download the file,,

Mobile site is developed using HTML and WCF, and the user ID and pwd present in different database application .

How to solve this ,

Thanks in advance..