Add Callback Endpoint to API

Geekbot.net/WebApi/Controllers/Callback/CallbackController.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Generic;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Threading.Tasks;
+using Discord.WebSocket;
+using Geekbot.net.Lib.GlobalSettings;
+using Microsoft.AspNetCore.Mvc;
+using Newtonsoft.Json;
+
+namespace Geekbot.net.WebApi.Controllers.Callback
+{
+    public class CallbackController : Controller
+    {
+        private readonly DiscordSocketClient _client;
+        private readonly IGlobalSettings _globalSettings;
+
+        public CallbackController(DiscordSocketClient client, IGlobalSettings globalSettings)
+        {
+            _client = client;
+            _globalSettings = globalSettings;
+        }
+        
+        [Route("/callback")]
+        public async Task<IActionResult> DoCallback([FromQuery] string code)
+        {
+            var token = "";
+            using (var client = new HttpClient())
+            {
+                client.BaseAddress = new Uri("https://discordapp.com");
+                var appInfo = await _client.GetApplicationInfoAsync();
+                var accessToken = _globalSettings.GetKey("OAuthToken");
+                var callbackUrl = _globalSettings.GetKey("OAuthCallbackUrl");
+
+                var form = new Dictionary<string, string>();
+                form.Add("client_id", appInfo.Id.ToString());
+                form.Add("client_secret", accessToken);
+                form.Add("grant_type", "authorization_code");
+                form.Add("code", code);
+                form.Add("scope", "identify email guilds");
+                form.Add("redirect_uri", callbackUrl);
+                
+                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/x-www-form-urlencoded"));
+                var result = await client.PostAsync("/api/oauth2/token", new FormUrlEncodedContent(form));
+                result.EnsureSuccessStatusCode();
+
+                var stringResponse = await result.Content.ReadAsStringAsync();
+                var responseData = JsonConvert.DeserializeObject<CallbackTokenResponseDto>(stringResponse);
+                token = responseData.access_token;
+            }
+
+            return new RedirectResult($"https://geekbot.pizzaandcoffee.rocks/login?token={token}", false);
+        }
+    }
+}

Geekbot.net/WebApi/Controllers/Callback/CallbackTokenResponseDto.cs

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+namespace Geekbot.net.WebApi.Controllers.Callback
+{
+    public class CallbackTokenResponseDto
+    {
+        public string access_token { get; set; }
+        public string token_type { get; set; }
+        public int expires_in { get; set; }
+        public string refresh_token { get; set; }
+        public string scope { get; set; }
+    }
+}