Hello,
I encounter the same issue as here https://www.reddit.com/r/networking/comments/4375w5/force_captive_portal_after_joining_wifi_network/
Behaviour with http redirection
The guest portal work on every devices (Android, IOS, Win10) except Win7. The guest user should use a http website to obtain the guest portal. Not acceptable, we cannot give support to all guest users using Win7. How is it working in airport, hospitals, universities, hotels ?
Behaviour with https redirection
There is a certificate warning on every devices ! Not acceptable. Some android devices tested (66%) don't allow to bypass the certificate warning.
Using WLC 8.5 and ISE 2.4 patch 5
Thanks for your help