Pier Unix style security: how do I let users login 'on the fly'?

Hello, I want to let users click on a URL, like mysite.com/seaside/pier/welcome/do_something?param1=xyz where viewing do_something needs a login and a parameter. If they are not logged in yet, I want them to login, using the PULogin command, and then do_something should be executed (without needing another click . What I do now is: mysite.com/seaside/pier/welcome?command=DoSomethingCommand&param1=xyz By changing the start: method I can let the command (my own PRCommand subclass DoSomethingCommand) capture the parameter param1 in an instance variable. I know that I can check context isLoggedIn inside DoSomethingCommand>>doValidate. But how do I transfer control to the PULogin command to give the user a login page, and then get back to do the rest of the validation for my command? Any pointers will be greatly appreciated :-) Matthias