How do I POST urlencoded form data with $http without jQuery?

I am new to AngularJS, and for a start, I thought to develop a new application using only AngularJS.

I am trying to make an AJAX call to the server side, using $http from my Angular App.

For sending the parameters, I tried the following:

$http({
    method: "post",
    url: URL,
    headers: {'Content-Type': 'application/x-www-form-urlencoded'},
    data: $.param({username: $scope.userName, password: $scope.password})
}).success(function(result){
    console.log(result);
});

This is working, but it is using jQuery as well at $.param. For removing the dependency on jQuery, I tried:

data: {username: $scope.userName, password: $scope.password}

but this seemed to fail. Then I tried params:

params: {username: $scope.userName, password: $scope.password}

but this also seemed to fail. Then I tried JSON.stringify:

data: JSON.stringify({username: $scope.userName, password: $scope.password})

I found these possible answers to my quest, but was unsuccessful. Am I doing something wrong? I am sure, AngularJS would provide this functionality, but how?