WebAPI not found

WebAPI not found

Sadly, I cannot get the most basic of things working with WebAPI
$.ajax({
url: "https://192.168.1.100/Api/Authentication/LogIn",
type: "POST",
contentType: "application/json",
data: "{ 'username': 'admin', 'password': 'MyPass' }",
error: function (r, s, e) { alert(e); },
success: function (d, s, r) { alert(s); }
});
I get "Not found"
API controller definition
public class AuthenticationController : ApiController
{
[HttpPost]
public bool LogIn(string username, string password)
{
return true;
}
}
If I remove HttpPost and replace it with HttpGet and then do
$.ajax({
url:
"https://192.168.1.100/Api/Authentication/LogIn?username=admin&password=MyPass",
type: "GET",
error: function (r, s, e) { alert(e); },
success: function (d, s, r) { alert(s); }
});
That works fine.
What's wrong with WebAPI?