CDRIVER-3502 Lift restriction on authSource without credentials (#841)

Author: alcaeus

src/libmongoc/src/mongoc/mongoc-uri.c

@@ -1339,7 +1339,6 @@ mongoc_uri_finalize_auth (mongoc_uri_t *uri,
    if (bson_iter_init_find_case (
           &iter, &uri->credentials, MONGOC_URI_AUTHSOURCE)) {
       source = bson_iter_utf8 (&iter, NULL);
-      require_auth = true;
    }
 
    if (mongoc_uri_get_auth_mechanism (uri)) {

src/libmongoc/tests/json/auth/connection-string.json

@@ -352,9 +352,10 @@
       "credential": null
     },
     {
-      "description": "authSource without username is invalid (default mechanism)",
+      "description": "authSource without username doesn't create credential (default mechanism)",
       "uri": "mongodb://localhost/?authSource=foo",
-      "valid": false
+      "valid": true,
+      "credential": null
     },
     {
       "description": "should throw an exception if no username provided (userinfo implies default mechanism)",

src/libmongoc/tests/json/connection_uri/additional-nonspec-tests.json

@@ -3,7 +3,7 @@
     {
       "description": "Repeated authSource key",
       "uri": "mongodb://example.com/?authSource=bar&authSource=foo",
-      "valid": false, 
+      "valid": true,
       "comment": "invalid URI (see SPEC-1424)",
       "warning": true,
       "hosts": [