Provides the ability to retrieve an Access Token via REST API

AzureRmAccessToken.cs

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Net.Http.Headers;
using Newtonsoft.Json;

namespace Example
{
    class Program
    {
        private static readonly HttpClient client = new HttpClient();

        static void Main(string[] args)
        {
            string tenantId = "";
            string clientId = "";
            string clientSecret = "";

            HttpResponseMessage response = null;
            string accessToken = "";

            FormUrlEncodedContent body = new FormUrlEncodedContent(new[]
            {
                new KeyValuePair<string, string>("grant_type", "client_credentials"),
                new KeyValuePair<string, string>("client_id", clientId),
                new KeyValuePair<string, string>("client_secret", clientSecret),
                new KeyValuePair<string, string>("resource", "https://management.azure.com/")
            });

            client.BaseAddress = new Uri("https://login.microsoftonline.com/");
            client.DefaultRequestHeaders.Accept.Clear();
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            try
            {
                response = client.PostAsync((tenantId + "/oauth2/token"), body).Result;
            } catch (Exception ex)
            {
                Console.WriteLine(ex);
            }

            if (response.IsSuccessStatusCode)
            {
                var content = response.Content.ReadAsStringAsync().Result;
                accessToken = JsonConvert.DeserializeObject<Response>(content).access_token;
            }
        }
    }

    public class Response
    {
        public string token_type { get; set; }
        public string expires_in { get; set; }
        public string ext_expires_in { get; set; }
        public string expires_on { get; set; }
        public string not_before { get; set; }
        public string resource { get; set; }
        public string access_token { get; set; }
    }
}