HTTP agent allows using non-HTTP scheme (make non HTTP(s) requests). For example, URL "ftp://your-server.here/" will work just fine and will return directory listing.

Currently there is no validation of scheme and this makes term HTTP agent invalid as it allows to make requests to: HTTP, FTP, POP3, IMAP, SMB, etc (https://curl.haxx.se/libcurl/c/CURLOPT_URL.html).

From the perspective of UI there are many fields that are not valid for FTP, POP3 and other protocols so for the sake of consistancy, scheme check should be introduced and only HTTP(s) scheme should be allowed in HTTP checks.