Redirection Plugin for Client Login?

Hello.. I am using the https://urbangiraffe.com/plugins/redirection/ plugin to redirect customer to another site for backend e-commerce photographic processing. Basically, I can provide customers with an extended URL, containing the name of their photo folder, as an addon from my WordPress Photocrati site… e.g. https://www.xxx.xxx/johnsmith.. The Johnsmith will in turn redirect them to my other site where I can do a more complete job of ecommerce and printing.

I would like to populate that extension as a part of client logon off the main site, similar to:

https://www.paulreiffer.com/client-login/

Has anyone seen something along those lines, or can recommend another way to accomplish the above? For a lot of reasons, I need to get them to the other site (Smugmug) to review their images and select which they’d like to print, etc. I appreciate any and all help.

Jay S.