Redirect internal link to external site

Okay, so my first observation here is that SNAT isn't relevant in an HTTP redirect situation. SNAT would be important if the traffic were flowing through the VIP to the application, but because you're redirecting, the remote service is going to get the client's source address.

Second, when a user accesses the trigger URL, gets redirected and then redirected again, and then lands on the remote site's page, what happens next? How does the user get back to your site? How does the remote site share information with your site?