Mon Apr 06, 2015 9:04 pm
Apparently, current versions of IE, windows 8, and Chrome all try to detect a captive portal. If they detect one, they open the login page without using ssl, so no security warning happens. If your users don't have https:// websites as their default page, then they won't get the problem either - the hotspot just redirects them.
The certificate warning happens when a client tries to open an ssl-protected website before doing anything else. The browser thinks it's going to "my secure website" - so when it gets a certificate from your hotspot server for "myhotspot.com - signed by verisign - 100% legitimate) it is correctly alarming the user: "Warning - you are talking to a web server that is not the one you asked for!"
Many people respond by asking: "But I'm redirecting them to myhotspot.com ssl login page, and my certificate is valid!"
"Why should the client's browser give warning?"
Redirect is a message that happens in the http protocol... certificates and ssl happen on port 443 BEFORE the http messages can begin. SSL starts by giving a certificate - before the client can ask for a website by name. So a browser sends TCP:443 packet to "google.com" and your Mikrotik answers in stead - SYN,ACK" - client acknowledges and starts the SSL request. The Mikrotik's certificate is for myhotspot.com - even if it is signed by Verisign, it is NOT the certificate for the web site that the client was asking for, so the browser will give a warning "certificate does not match website" - if the user clicks "do it anyway" - only THEN does the browser say "I want http 1.1, host=google.com, etc - " to which your Mikrotik finally gets to respond with the redirect header: "site moved to myhotspot.com"
Only a valid certificate signed by a trusted authority, matching the website you requested will work.
Jumping in the middle will break one of these - so there will be a warning, or else you could just as easily intercept connections to the users' banking websites without any warnings.....
So this is why it's good that browsers and operating systems are starting to check for a hotspot as soon as the device joins the network. If the device knows it's on a hotspot, it can open a non-ssl browser window and let the hotspot direct to the login page without any SSL warnings.