Get protocol correctly if using SSL direct to Mattermost (#6361)

app/login.go

@@ -138,7 +138,7 @@ func DoLogin(w http.ResponseWriter, r *http.Request, user *model.User, deviceId
 }
 
 func GetProtocol(r *http.Request) string {
-	if r.Header.Get(model.HEADER_FORWARDED_PROTO) == "https" {
+	if r.Header.Get(model.HEADER_FORWARDED_PROTO) == "https" || r.TLS != nil {
 		return "https"
 	} else {
 		return "http"