internal auth & authorization

* do not handle authorization from internal sources
* do not remove authorization from internal sources

* when connecting to external from internal, a 401/407 may be returned
  and we relay that info back to media server, which will issue a new request
  with authorization, and we need to pass that info to external

(cherry picked from commit 69df3e373d)

kamailio/authorization.cfg

@@ -79,6 +79,11 @@ route[AUTHORIZATION_CHECK_REGISTERED]
 route[HANDLE_AUTHORIZATION]
 {
 
+    if (isflagset(FLAG_INTERNALLY_SOURCED)) {
+        route(MAIN);
+        exit;
+    }
+
     if(!is_present_hf("Proxy-Authorization")) {
         route(MAIN);
         exit;

kamailio/default.cfg

@@ -251,9 +251,10 @@ route
 
 route[MAIN]
 {
-    route(AUTHORIZATION);
-
-    remove_hf("Authorization");
+    if (!isflagset(FLAG_INTERNALLY_SOURCED)) {
+        route(AUTHORIZATION);
+        remove_hf("Authorization");
+    }
 
     #!ifdef MESSAGE_ROLE
     route(HANDLE_MESSAGE);