Cross site login script

1

please help me logging to cross site.

i have few domains with 1 user system. i’m trying to have a login script past few days sharing sessions. if i use $_GET i could solve it easily. but i don’t want it.
is there any other way? any idea? any experience?

forexample:

  1. www.domain1.com , www.domain2.com
  2. if i login using my id at www.domain1.com then i also should be logged at www.domain2.com automatically.

P.S:

  1. i use adodb.
  2. i have tried to use iframe. but mostly it was unsuccessful.
  3. past few days i read about cookie so many times and google-d about it. but all of them were unsuccessful too.

Thank you.