Fix message when username field not exists in OAuth data

Closes #5221

packages/rocketchat-custom-oauth/custom_oauth_server.js

@@ -224,14 +224,14 @@ export class CustomOAuth {
 		if (this.usernameField.indexOf('#{') > -1) {
 			username = this.usernameField.replace(/#{(.+?)}/g, function(match, field) {
 				if (!data[field]) {
-					throw new Meteor.Error(`Username template item "${field}" not found in data`, data);
+					throw new Meteor.Error('field_not_found', `Username template item "${field}" not found in data`, data);
 				}
 				return data[field];
 			});
 		} else {
 			username = data[this.usernameField];
 			if (!username) {
-				throw new Meteor.Error(`Username field "${this.usernameField}" not found in data`, data);
+				throw new Meteor.Error('field_not_found', `Username field "${this.usernameField}" not found in data`, data);
 			}
 		}