How to access Angular's Optional Configuration Object for $http.get in ASP.net

Question

I have a URL that looks like this:

example.com/users/34/

I want for Angular to be able to take this ID (34) and make a call to my ASP.net server to grab information about that user.

As per Angular's documentation (https://docs.angularjs.org/api/ng/service/$http#get) I am thinking I should be able to do something like this in order to achieve that:

$http.get("/api/users/", { UserID: 34 } ).
success(function (user, status, headers, config) {
    console.log(user);
}).
error(function (data, status, headers, config) {
    console.log(status);
});

But I cannot manage to write an ASP.net function that is able to grab the UserID variable. Here's what my C# function looks like at the moment:

[Route("api/users")]
public HttpResponseMessage getUser()
{
  // do some stuff... but where is UserID? I can't find it in the header etc
}

When I set up a break point, that function fires successfully, but I cannot get UserID. Looking around and can't seem to find any documentation on this.

Any ideas?

--- Update ---

I've confirmed that this works:

Inside my Angular file:

$http.get("/api/users/?UserID=34" ).
success(function (user, status, headers, config) {
    console.log(user);
}).
error(function (data, status, headers, config) {
    console.log(status);
});

Inside my C# file:

[Route("api/users")]
public HttpResponseMessage getUser( int UserID )
{
  // yay! UserID now equals 34
}

But what I would like to do instead of passing the variable as part of the URL string, is pass it as an Optional configuration object (as per https://docs.angularjs.org/api/ng/service/$http#get).

That's what I am asking help with.