Kindly I need your guide to implement this difficult task , I am newcomer to java ..

my manager assigned me really difficult task
web page to bypass the proxy server of our company
our company dedicated ISA proxy server to filter web surfing and also downloading and setting Quota by it
the task how to send HTTPrequest through my webpage with other userName and password than Windows ones to grant me full access to internet
for example : if my windows userName x ) and x is granted little permissions to surf and download from the internet , then I want my webpage to allow user to input the URL and then sending the HTTP request through the proxy with other user than X , with the user Y (for example) who has full access to the internet ... that means I have authentication (userName & password) which I want to put it as constants on my code to grant any user using my webpage full access to internet

how could I do such task.........
I will be very appreciated for your kind help