$scope.login = function() {
            $http({
              method: 'POST',
              data: {
                username: $scope.username,
                password: $scope.password
              },
              url: 'http://127.0.0.1:5000/login/'
            }).then(function successCallback(response) {
                console.log('successCallback')
              }, function errorCallback(response) {
                console.log('errorCallback')
              });
}

XMLHttpRequest cannot load http://127.0.0.1:5000/login/. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access.