I redirect all my hotspot captive portal files to an external server with its own SSL cert. When sending the login form back to MikroTik to instigate a login , I get a warning that the data is not secure as its coming from an SSL site, posted to HttP: site (10.5.50.1)
Ive found another way around this problem , transfering the login credentials from the website to a non ssl page on the same server using the session variables, and then posting the non ssl version back to Mikrotik. Password is encrypted anyhow so non SSL authentication is fine.
Users are happier though usingg SSL on the main sign up pages and save me the hassle of having loads of SSL certs to pay for (self signed not being an option)
You can use wildcard certs just fine, or alternatively use the same internal DNS name everywhere. I use hotspot.company.com mapped to 10.1.0.1 and have a VLAN interface on all Hotspot routers that carries that IP address. Bought one cert for that name, and use it on all my Hotspot routers.