A null config value for "verification_code" will show a console prompt. This allows Environment.GetEnvironmentVariable to be used directly as config callback.

Examples/Program_DownloadSavedMedia.cs

@@ -9,17 +9,11 @@ namespace WTelegramClientTest
 {
 	class Program_DownloadSavedMedia
 	{
-		static string Config(string what)
-		{
-			// go to Project Properties > Debug > Environment variables and add at least these: api_id, api_hash, phone_number
-			if (what == "verification_code") { Console.Write("Code: "); return Console.ReadLine(); }
-			return Environment.GetEnvironmentVariable(what);
-		}
-
+		// go to Project Properties > Debug > Environment variables and add at least these: api_id, api_hash, phone_number
 		static async Task Main(string[] args)
 		{
 			Console.WriteLine("The program will download photos/medias from messages you send/forward to yourself (Saved Messages)");
-			using var client = new WTelegram.Client(Config);
+			using var client = new WTelegram.Client(Environment.GetEnvironmentVariable);
 			await client.ConnectAsync();
 			var user = await client.LoginUserIfNeeded();
 			client.Update += Client_Update;
@@ -34,7 +28,7 @@ namespace WTelegramClientTest
 						continue; // if it's not a new saved message, ignore it
 					if (message.media is MessageMediaDocument { document: Document document })
 					{
-						int slash = document.mime_type.IndexOf('/'); // quick & dirty conversion from Mime to extension
+						int slash = document.mime_type.IndexOf('/'); // quick & dirty conversion from MIME type to file extension
 						var filename = slash > 0 ? $"{document.id}.{document.mime_type[(slash + 1)..]}" : $"{document.id}.bin";
 						Console.WriteLine("Downloading " + filename);
 						using var fileStream = File.Create(filename);
@@ -50,7 +44,7 @@ namespace WTelegramClientTest
 						fileStream.Close(); // necessary for the renaming
 						Console.WriteLine("Download finished");
 						if (type is not Storage_FileType.unknown and not Storage_FileType.partial)
-							File.Move(filename, Path.ChangeExtension(filename, type.ToString())); // rename extension
+							File.Move(filename, $"{photo.id}.{type}"); // rename extension
 					}
 				}
 			}

Examples/Program_ListenUpdates.cs

@@ -8,18 +8,12 @@ namespace WTelegramClientTest
 {
 	class Program_ListenUpdates
 	{
-		static string Config(string what)
-		{
-			// go to Project Properties > Debug > Environment variables and add at least these: api_id, api_hash, phone_number
-			if (what == "verification_code") { Console.Write("Code: "); return Console.ReadLine(); }
-			return Environment.GetEnvironmentVariable(what);
-		}
-
+		// go to Project Properties > Debug > Environment variables and add at least these: api_id, api_hash, phone_number
 		static async Task Main(string[] _)
 		{
 			Console.WriteLine("The program will display updates received for the logged-in user. Press any key to terminate");
 			WTelegram.Helpers.Log += (l, s) => System.Diagnostics.Debug.WriteLine(s);
-			using var client = new WTelegram.Client(Config) { CollectAccessHash = true };
+			using var client = new WTelegram.Client(Environment.GetEnvironmentVariable);
 			client.Update += Client_Update;
 			await client.ConnectAsync();
 			var my = await client.LoginUserIfNeeded();

README.md

@@ -46,16 +46,18 @@ static string Config(string what)
     if (what == "api_id") return "YOUR_API_ID";
     if (what == "api_hash") return "YOUR_API_HASH";
     if (what == "phone_number") return "+12025550156";
-    if (what == "verification_code") { Console.Write("Code: "); return Console.ReadLine(); }
-    if (what == "first_name") return "John";   // if sign-up is required
-    if (what == "last_name") return "Doe";     // if sign-up is required
-    if (what == "password") return "secret!";  // if user has enabled 2FA
+    if (what == "verification_code") return null; // let WTelegramClient ask the user with a console prompt 
+    if (what == "first_name") return "John";      // if sign-up is required
+    if (what == "last_name") return "Doe";        // if sign-up is required
+    if (what == "password") return "secret!";     // if user has enabled 2FA
     return null;
 }
 ...
 using var client = new WTelegram.Client(Config);
 ```
-There are other configuration items that are queried to your method but returning `null` let WTelegramClient choose a default adequate value. Those shown above are the only ones that have no default values and are required to be provided by your method.
+There are other configuration items that are queried to your method but returning `null` let WTelegramClient choose a default adequate value. Those shown above are the only ones that have no default values and should be provided by your method.
+
+Another simpler approach is to pass `Environment.GetEnvironmentVariable` as the config callback and define the above items as environment variables.
 
 Finally, if you want to redirect the library logs to your logger instead of the Console, you can install a delegate in the `WTelegram.Helpers.Log` static property.
 Its `int` argument is the log severity, compatible with the classic [LogLevel enum](https://docs.microsoft.com/en-us/dotnet/api/microsoft.extensions.logging.loglevel)

src/Client.cs

@@ -101,13 +101,14 @@ namespace WTelegram
 			"lang_pack" => "",
 			"lang_code" => CultureInfo.CurrentUICulture.TwoLetterISOLanguageName,
 			"user_id" => "-1",
-			_ => null // api_id api_hash phone_number verification_code... it's up to you to reply to these correctly
+			"verification_code" => AskConfig(config),
+			_ => null // api_id api_hash phone_number... it's up to you to reply to these correctly
 		};
 
-		public static string DefaultConfigOrAsk(string config)
+		public static string DefaultConfigOrAsk(string config) => DefaultConfig(config) ?? AskConfig(config);
+
+		private static string AskConfig(string config)
 		{
-			var value = DefaultConfig(config);
-			if (value != null) return value;
 			Console.Write($"Enter {config.Replace('_', ' ')}: ");
 			return Console.ReadLine();
 		}