Authentication problem!

[Remco]

Hello,

here is my problem!:

At our website a user will be validated for visiting certain pages.
We use a login.asp page which checks a database if the user is permitted to
view the pages he wants to see!

We also have a agreement with a other company to redirect to their website.
So if our user is logged in he must be able to visit the third part
website!!

The third part website is protected with a username and password.
We don't want our visitor to type in the username and password because we
don't want him to know this.

How we handle this all:

User is clicking to a certain hyperlink -> a page at our server is tracing
if the user is logged in, if he is, we redirect him to the third part!!
Then the window for authentication is popping up!!! (And that's exactly what
we don't want) -:)

Do you have a solution for this "maybe with W3 Sockets" or can we do
authentication on an other way.

We also tried to do this by grabbing the REMOTE_ADDR from the header
(Because we redirect server side, i thought this would be the number of our
server,
but it is still the number of the user).

Hope to hear a solution!

Thanks in advance
Remco