chaosbot/ChaosBot/WebServer/App/DiscordController.cs

using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Newtonsoft.Json;
using NLog;

namespace ChaosBot.WebServer.App
{
    [ApiController]
    [Route("/api/discord")]
    public class DiscordController : Controller
    {
        private static readonly HttpClient client = new HttpClient();
        private static readonly ILogger Logger = Program.Logger;
        
        [HttpGet]
        public async Task<IActionResult> Index(string code = null)
        {
            string redirectUri = $"{Program.AppSettingsHandler.GetValue<string>("Discord:BaseUri")}/api/discord";
            string clientId = Program.AppSettingsHandler.GetValue<string>("Discord:ClientId");
            string clientSecret = Program.AppSettingsHandler.GetValue<string>("Discord:ClientSecret");
            
            if (code == null)
                return Redirect($"https://discord.com/api/oauth2/authorize?client_id={clientId}&redirect_uri={redirectUri}&response_type=code&scope=identify%20guilds");

            Dictionary<string, string> values = new Dictionary<string, string>
            {
                { "client_id", clientId },
                { "client_secret", clientSecret },
                { "grant_type", "authorization_code" },
                { "code", code },
                { "redirect_uri", redirectUri },
                { "scope", "identify guild" }
            };

            FormUrlEncodedContent content = new FormUrlEncodedContent(values);
            HttpResponseMessage response = await client.PostAsync("https://discord.com/api/oauth2/token", content);
            string responseString = await response.Content.ReadAsStringAsync();
            DiscordOauthResponse responseObject = JsonConvert.DeserializeObject<DiscordOauthResponse>(responseString);

            return LocalRedirect($"/#/?access_token={responseObject.access_token}");
        }

        [HttpGet("user")]
        public IActionResult GetUser()
        {
            if (!Request.Cookies.TryGetValue("access_token", out string accessToken))
                accessToken = null;

            HttpResponseMessage response;
            using (HttpRequestMessage requestMessage =
                new HttpRequestMessage(HttpMethod.Get, "https://discord.com/api/v7/users/@me"))
            {
                requestMessage.Headers.Authorization =
                    new AuthenticationHeaderValue("Bearer", accessToken);
                response = client.SendAsync(requestMessage).GetAwaiter().GetResult();
            }
            string responseString = response.Content.ReadAsStringAsync().GetAwaiter().GetResult();
            DiscordUserResponse userResponse = JsonConvert.DeserializeObject<DiscordUserResponse>(responseString);

            return Json(userResponse);
        }

        [HttpGet("guilds")]
        public IActionResult GetGuilds()
        {
            if (!Request.Cookies.TryGetValue("access_token", out string accessToken))
                accessToken = null;

            HttpResponseMessage response;
            using (HttpRequestMessage requestMessage =
                new HttpRequestMessage(HttpMethod.Get, "https://discord.com/api/v7/users/@me/guilds"))
            {
                requestMessage.Headers.Authorization =
                    new AuthenticationHeaderValue("Bearer", accessToken);
                response = client.SendAsync(requestMessage).GetAwaiter().GetResult();
            }
            string responseString = response.Content.ReadAsStringAsync().GetAwaiter().GetResult();
            List<DiscordGuildResponse> userResponse = JsonConvert.DeserializeObject<List<DiscordGuildResponse>>(responseString);

            return Json(userResponse);
        }
    }

    internal class DiscordOauthResponse
    {
        public string error { get; set; } = null;
        public string error_description { get; set; } = null;
        public string access_token { get; set; } = null;
        public int expires_in { get; set; } = 0;
        public string refresh_token { get; set; } = null;
        public string scope { get; set; } = null;
        public string token_type { get; set; } = null;
    }

    public class DiscordUserResponse
    {
        public string id { get; set; }
        public string username { get; set; }
        public string discriminator { get; set; }
        public string avatar { get; set; } = null;
        public bool bot { get; set; } = false;
        public bool system { get; set; } = false;
        public bool mfa_enabled { get; set; } = false;
        public string locale { get; set; } = null;
        public bool verified { get; set; } = false;
        public string email { get; set; } = null;
        public int flags { get; set; } = 0;
        public int premium_type { get; set; } = 0;
        public int public_flags { get; set; } = 0;
    }

    public class DiscordGuildResponse
    {
        public string id { get; set; }
        public string name { get; set; }
        public string icon { get; set; }
        public bool owner { get; set; }
        public int permissions { get; set; }
        public int permissions_new { get; set; }
    }
}