public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        ...

        var cors = new EnableCorsAttribute("*", "*", "*");

        config.EnableCors(cors);

        ...

    }
}

loginUser(username: string, password: string) {
    let serviceURL = 'http://myurl/token';

    let body = 'username=' + username + '&password=' + password + '&grant_type=password';

    let headers: Headers = new Headers();
    headers.append('Content-Type', 'application/x-www-form-urlencoded');

    let options: RequestOptions = new RequestOptions({
        headers: headers
    });

    return this.http.post(serviceURL, body, options)
        .map(res => this.extractData(res))
        .catch(this.handleError);
}