Need to create irule that can redirect a port to another port

I thought about creating the other VS, however the developers are saying we have to remove the port because the initial request is on port80 and the cookie will get assign on that port. If I create the other VS and it goes to port 9081, then the user will need to re-authenticate because the cookie session will be invalid. It's the way the application works, I hate it. If you know how to write the irule that would be awesome.