Added ability to force verify on twitch authentication (#202)

src/Owin.Security.Providers.Twitch/TwitchAuthenticationHandler.cs

@@ -179,6 +179,7 @@ namespace Owin.Security.Providers.Twitch
                 "?client_id=" + Uri.EscapeDataString(Options.ClientId) +
                 "&redirect_uri=" + Uri.EscapeDataString(redirectUri) +
                 "&scope=" + Uri.EscapeDataString(scope) +
+                "&force_verify=" + Options.ForceVerify.ToString().ToLower() +
                 "&response_type=" + "code" +
                 "&state=" + Uri.EscapeDataString(state);
 

src/Owin.Security.Providers.Twitch/TwitchAuthenticationOptions.cs

@@ -120,6 +120,11 @@ namespace Owin.Security.Providers.Twitch
         /// </summary>
         public ISecureDataFormat<AuthenticationProperties> StateDataFormat { get; set; }
 
+        /// <summary>
+        ///     Gets or sets whether to force verify the user during the OAuth flow
+        /// </summary>
+        public bool ForceVerify { get; set; }
+
         /// <summary>
         ///     Initializes a new <see cref="TwitchAuthenticationOptions" />
         /// </summary>