Maybe this is mission impossible...but here we go:
I have a website aaa.com where clients fill in some web forms, then my app will generate some data...the next step is to send that data(i.e. by POST) to bbb.com...after that i should send the client to bbb.com. In bbb.com the client will finalize his job(i.e. submit generated data).
About bbb.com: they are using jsessionid(cookie).
I'm using GAE(google app engine, python).
How can i do that? I need some hints!