Two IIS, same domain, single sign on?

Hi,

I'm not sure if this is a simple request or something a bit more complicated, but here goes!

I've 2 IIS 8.5 servers on 2 separate Windows Servers linked to the same domain.  Users can log onto either webserver by using a windows authentication from the domain.  Unfortunately, a site on IIS2 want's to link to pages on IIS1, this means that the user is asked for their ID and password for IIS 1 (which is the same for IIS2).

Is there a way of authenticating on both servers at the same time or passing the login information from IIS2 to IIS1?

Thanks for any help.

Andy.