Add guard data to auth sample

Samples/1a.Authentication/Program.cs

@@ -12,6 +12,7 @@
 // save our logon details
 var user = args[ 0 ];
 var pass = args[ 1 ];
+string previouslyStoredGuardData = null; // For the sake of this sample, we do not persist guard data
 
 // create our steamclient instance
 var steamClient = new SteamClient();
@@ -48,25 +49,43 @@ async void OnConnected( SteamClient.ConnectedCallback callback )
 {
     Console.WriteLine( "Connected to Steam! Logging in '{0}'...", user );
 
+    var shouldRememberPassword = false;
+
     // Begin authenticating via credentials
     var authSession = await steamClient.Authentication.BeginAuthSessionViaCredentialsAsync( new AuthSessionDetails
     {
         Username = user,
         Password = pass,
-        IsPersistentSession = false,
+        IsPersistentSession = shouldRememberPassword,
+
+        // See NewGuardData comment below
+        GuardData = previouslyStoredGuardData,
+
+        /// <see cref="UserConsoleAuthenticator"/> is the default authenticator implemention provided by SteamKit
+        /// for ease of use which blocks the thread and asks for user input to enter the code.
+        /// However, if you require special handling (e.g. you have the TOTP secret and can generate codes on the fly),
+        /// you can implement your own <see cref="SteamKit2.Authentication.IAuthenticator"/>.
         Authenticator = new UserConsoleAuthenticator(),
     } );
 
     // Starting polling Steam for authentication response
     var pollResponse = await authSession.PollingWaitForResultAsync();
 
+    if ( pollResponse.NewGuardData != null )
+    {
+        // When using certain two factor methods (such as email 2fa), guard data may be provided by Steam
+        // for use in future authentication sessions to avoid triggering 2FA again (this works similarly to the old sentry file system).
+        // Do note that this guard data is also a JWT token and has an expiration date.
+        previouslyStoredGuardData = pollResponse.NewGuardData;
+    }
+
     // Logon to Steam with the access token we have received
     // Note that we are using RefreshToken for logging on here
     steamUser.LogOn( new SteamUser.LogOnDetails
     {
         Username = pollResponse.AccountName,
         AccessToken = pollResponse.RefreshToken,
-        ShouldRememberPassword = false, // If you set IsPersistentSession to true, this also must be set to true for it to work correctly
+        ShouldRememberPassword = shouldRememberPassword, // If you set IsPersistentSession to true, this also must be set to true for it to work correctly
     } );
 
     // This is not required, but it is possible to parse the JWT access token to see the scope and expiration date.