C# HttpClient proxy with username and password

Steps

1. Create a console project

   dotnet --version confirms the SDK. The template writes a Program.cs with implicit usings, so each example below adds a single using line, which brings in WebProxy and NetworkCredential. Replace Program.cs with an example and start it with dotnet run.

   dotnet --version
   dotnet new console -o ProxyCheck
   cd ProxyCheck

2. Give the handler a WebProxy with credentials

   WebProxy takes the proxy as http://HOST:PORT, and its Credentials property carries USERNAME and PASSWORD. UseProxy defaults to true; it is written out because a handler with UseProxy set to false ignores its Proxy without complaint. HttpClient.Timeout caps each request, the tunnel setup included.

   using System.Net;
   
   var handler = new HttpClientHandler
   {
       Proxy = new WebProxy("http://HOST:PORT")
       {
           Credentials = new NetworkCredential("USERNAME", "PASSWORD"),
       },
       UseProxy = true,
   };
   
   using var client = new HttpClient(handler) { Timeout = TimeSpan.FromSeconds(30) };
   
   var response = await client.GetAsync("https://api.ipify.org?format=json");
   Console.WriteLine($"{(int)response.StatusCode} {await response.Content.ReadAsStringAsync()}");

3. Run it and read the exit address

   dotnet run builds and starts the project, which prints 200 and the JSON from api.ipify.org. The test proxy logged two CONNECT requests: the first without a login, refused with 407, then a second carrying it. The handler deals with that challenge on its own.

4. Keep one HttpClient per proxy

   A new HttpClient disposed after every request closes its connection each time, and each closed socket sits in TIME_WAIT for a while afterwards. Under steady load the machine can run out of local ports, which surfaces as connection errors that have nothing to do with the proxy. Create clients once and reuse them for the life of the program.

5. Rotate across static IPs with SocketsHttpHandler

   This second Program.cs reads proxies.txt from the project folder, one HOST:PORT:USERNAME:PASSWORD line per fixed IP, and builds a SocketsHttpHandler with its own HttpClient for each line. ConnectTimeout bounds the connection to the proxy, and PooledConnectionLifetime retires pooled connections after five minutes. Request i goes to client i modulo the list length; a proxy that fails prints its message and the others carry on.

   using System.Net;
   
   var clients = File.ReadLines("proxies.txt")
       .Where(line => !string.IsNullOrWhiteSpace(line))
       .Select(line =>
       {
           var p = line.Trim().Split(':', 4);
           var handler = new SocketsHttpHandler
           {
               Proxy = new WebProxy(p[0], int.Parse(p[1]))
               {
                   Credentials = new NetworkCredential(p[2], p[3]),
               },
               UseProxy = true,
               ConnectTimeout = TimeSpan.FromSeconds(10),
               PooledConnectionLifetime = TimeSpan.FromMinutes(5),
           };
           return new HttpClient(handler) { Timeout = TimeSpan.FromSeconds(30) };
       })
       .ToList();
   
   for (var i = 0; i < 6; i++)
   {
       var client = clients[i % clients.Count];
       try
       {
           Console.WriteLine($"{i} {await client.GetStringAsync("https://api.ipify.org")}");
       }
       catch (Exception e) when (e is HttpRequestException or TaskCanceledException)
       {
           Console.WriteLine($"{i} {e.Message}");
       }
   }

Common errors and fixes

Which line to pick

C# services that call APIs or fetch pages in volume stay cheapest on datacenter IPs wherever the target accepts them. Switch to residential once server ranges get refused, and pin a long-running worker to an ISP IP when it needs the same address across sessions.

Other setup guides

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