Add Client-ID header to Twitch Helix API requests (#420)

Resolves #419.

Author: kinosang

src/AspNet.Security.OAuth.Twitch/TwitchAuthenticationConstants.cs

@@ -20,5 +20,10 @@ public static class Claims
             public const string ProfileImageUrl = "urn:twitch:profileimageurl";
             public const string Type = "urn:twitch:type";
         }
+
+        public static class Headers
+        {
+            public const string ClientId = "Client-ID";
+        }
     }
 }

src/AspNet.Security.OAuth.Twitch/TwitchAuthenticationHandler.cs

@@ -48,6 +48,7 @@ protected override async Task<AuthenticationTicket> CreateTicketAsync([NotNull]
             var request = new HttpRequestMessage(HttpMethod.Get, Options.UserInformationEndpoint);
             request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
             request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", tokens.AccessToken);
+            request.Headers.Add(TwitchAuthenticationConstants.Headers.ClientId, Options.ClientId);
 
             var response = await Backchannel.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, Context.RequestAborted);
             if (!response.IsSuccessStatusCode)