You could do this in several ways...
Let's say that page1 sends usr+psw to page2
Page 2 will to whatever, and this page will call the
page3 passing the usr+psw+whatever to page3.
(at least that's what I have understood on your request)
So page2 could call page3 in:
. <META HTTP-EQUIV=Refresh CONTENT="0; URL=http://site.com/page3.php?var1=123&var2=123">
The bas side of this is that variables are then seen in the url field. But a hashing of them, or even encrytion can solve that issue.
. header("Location: [site.com...] This will work in all browsers, but has the same problem as above.
Hope it helps.