Use use username and not user for auth.

Author: aljones15

lib/authn.js

@@ -128,7 +128,7 @@ async function _isAuthnRequired({config, admin}) {
 
 function _addAuthOptions({options, config}) {
   options.connectOptions.auth = {
-    user: config.username,
+    username: config.username,
     password: config.password
   };
   // authSource is the database to authenticate against