User authentication between two asp.net websites

[shil]

Hi,

Is there any possibility to authenticate an user between two websites?
I have a website through which users login and get authenticated. In
the same website I link to a different website and would like to pass
userid to the second website. My question is I want to restrict users
from going to the second website directly without getting authenticated
from the first one. Is this possible?

I know we can do this using Forms Authentication if this is in one
website.
I used below code in the web.config file of second website.

<authentication mode="Forms">
<forms name="Upgrade"
loginUrl="http://www.firstwebsite.com/TestDirectory/Login.aspx"
protection="All" path="/">
</forms>
</authentication>

When I go to the second one directly, I get an error as below

******************************
The resource cannot be found.
Description: HTTP 404. The resource you are looking for (or one of its
dependencies) could have been removed, had its name changed, or is
temporarily unavailable. Please review the following URL and make sure
that it is spelled correctly.

Requested Url: /TestDirectlry/Login.aspx
******************************

Which appears the website is looking for /TestDirectory/Login.aspx in
the second web project.

Any help is appreciated.

Thanks.