Why does captive portal detection use HTTP?
Many Wi‑Fi networks use a special “captive portal” page for login/terms before granting internet access. Because HTTPS is encrypted by default,
captive portals typically intercept unencrypted HTTP traffic to show the login page. If the site you try to reach first uses HTTPS, the portal may fail to redirect.
You can test with a plain HTTP URL such as http://captive.uihhotspot.com.