calling one page and passing values from codebehind

i want to open website by clicking on one button and open its inner page with automatically passing login details from static string. 
for example on button_click following thing should be happen
i am having username and password in string like string unm="abc"; string pwd="xyx";
now i want to write code for opening facebook.com page and pass username and password and automatically press login button.
and inner page should open.
this thing should be on button click  means if you click on button without entring userame password and pressign login button it should get enterd in fb