Architectural Question

[Guest]

I am seeking your advices. I have site A and Site B both using Forms
authentication. My user logs in to Site A, I want to show Site B default.aspx
page somewhere in Site A default.aspx page (lets say in a web part). This
includes automatically authenticating my user to site B and linking to its
default.aspx page. What is the best approach?

Thanks a lot for your time