Iniciar sesión en el sitio web en C#

public static string HttpGet(string web_URI) {
  System.Net.WebRequest web_request = System.Net.WebRequest.Create(web_URI);

  // the following means no proxy for the website
  web_request.Proxy = new System.Net.WebProxy(ProxyString, true);

  System.Net.WebResponse web_response = web_request.GetResponse();

  System.IO.StreamReader stream_reader =
      new System.IO.StreamReader(web_response.GetResponseStream());

  return stream_reader.ReadToEnd().Trim();
}

public static string HttpPost(string web_URI, string web_para) {
  System.Net.WebRequest web_request = System.Net.WebRequest.Create(web_URI);
  web_request.Proxy = new System.Net.WebProxy(ProxyString, true);

  // add the following as you are doing the `POST`
  web_request.ContentType = "your_application/insert-the-form-rncoded-URL";
  web_request.Method = "POST";  // SET

  // it's important to know how many bytes you are transforming or sending to the server.
  // Remember | Post'ed Faked Forms should be `name=value&`
  byte[] sending_bytes = System.Text.Encoding.ASCII.GetBytes(web_para);
  web_request.ContentLength = sending_bytes.Length;

  System.IO.Stream web_stream = web_request.GetRequestStream();

  // you can push the bytes here
  web_stream.Write(sending_bytes, 0, sending_bytes.Length);
  web_stream.Close();

  System.Net.WebResponse web_response = web_request.GetResponse();
  if (web_response == null)
    return null;

  System.IO.StreamReader stream_reader =
      new System.IO.StreamReader(web_response.GetResponseStream());

  return stream_reader.ReadToEnd().Trim();
}

field_1 = value_1 & field_2 = value_2

// the `web_URL` represents the `POST` URL instead of the `form` URL
// to access `form` URL, find the `action` attribute of the HTML's `form` tag
string web_URL =
    "http://www.examplewebsite.com/index.do?PageModule=UserAccess&Modification=UsersVerificationviaLogin";

string parameter_form = string.Format("example_format(email_address={0}&password={1})",
                                      "my_email_address", "my_password");

// create a header cookie
string header_cookie;

// create a request object from the `WebRequest`
WebRequest web_request = WebRequest.Create(web_URL);

// define its content type and method
web_request.ContentType =
    "yourC#application/x-www_address-form-encoded_url";  // or something like
                                                         // "application/x-www-form-urlencoded"
web_request.Method = "POST";  // as it's a request, so the method will be POST

// access the `parameter_form` to convert it into bytes (sending it to the server)
byte[] sending_bytes = Encoding.ASCII.GetBytes(parameter_form);
web_request.ContentLength = sending_bytes.Length;  // define its length

using (Stream web_stream = web_request.GetRequestStream()) {
  // for web requests or requests to the server for login
  web_stream.Write(sending_bytes, 0, sending_bytes.Length);
}

// create a `WebResponse` object to receive or understand the response from the corresponding server
WebResponse web_response = web_request.GetResponse();
header_cookie = web_response.Headers["Set-cookie"];  // `Set-cookie` as a web response header file

/*
    GET
*/

// define a source page and the `GET` web URL
string source_page;
string web_URL_get =
    "http://www.webpage_behind_the_login.com";  // mention the webpage behind the login form

// create a GET response
WebRequest web_request_get = WebRequest.Create(web_URL_get);
web_request_get.Headers.Add("Cookie", header_cookie);

// web_request_get.ContentLength = web_request.ContentLength;
WebResponse web_response_get = web_request_get.GetResponse();

using (StreamReader stream_reader_get = new StreamReader(web_response_get.GetResponseStream())) {
  source_page = stream_reader_get.ReadToEnd();
}

using System;
using System.Windows.Forms;
using System.Net;
// using System.Net.Http;
using System.Collections.Specialized;

namespace test_login {
  // create a sub-class using `WebClient`
  public class CookieAwareWebClient : WebClient {
    // create a cookie container for web requests and web response
    private CookieContainer website_cookie = new CookieContainer();

    // overload using URI of the target web address
    protected override WebRequest GetWebRequest(Uri trg_web_add) {
      WebRequest tag_web_request = base.GetWebRequest(trg_web_add);
      if (tag_web_request is HttpWebRequest) {
        (tag_web_request as HttpWebRequest).CookieContainer =
            website_cookie;  // generate a proper request to the server
      }
      return tag_web_request;
    }
  }
  public partial class Form1 : Form {
    public Form1() {
      InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e) {
      // create a new user
      var new_user = new CookieAwareWebClient();

      // base address of the corresponding webpage (for login)
      new_user.BaseAddress = @"https://www.example_website/some_page/login/url_address/";

      // create a variable that carries the user information
      var user_info = new NameValueCollection();
      user_info.Add("username", "your_username");  // username or mail address
      user_info.Add("password", "your_password");  // password

      // upload the user information to the webpage
      new_user.UploadValues("login_page.php", "POST", user_info);

      // successfully login can request the pages, following
      string source_html = new_user.DownloadString("website_homepage.php");
    }
  }
}

username: your_username
password: your_password

[redirect the user to the `index.php` after a successful login]

request.UserAgent = UserAgent;

// to eliminate any redirection to other website or webpage
request.AllowAutoRedirect = false;

using System;
using System.Windows.Forms;
using System.Net;
// using System.Net.Http;
using System.IO;
// using System.Collections.Specialized;

namespace test_login {
  public partial class Form1 : Form {
    public Form1() {
      InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e) {
      string user_name = UsernameBox.Username;              // textbox that contains the user name
      string user_password = PasswordBoxPassword.Password;  // textbox that contains the password

      // HTML IDs or important user information to perform a successful login against a specific
      // user
      string login_user_name = textBox1.Text;      // username
      string login_user_password = textBox2.Text;  // password

      // submit info for a successful login
      string login_submit_info = textBox3.Text;  // login submit

      // define the website or webpage connection parameters
      string post_method = "POST";  // `POST` method for web_request
      string type_webcontent = @"c_sharp-application/encoded_url-www-form";
      string string_login = login_user_name + "=" + user_name + "&" + login_user_password + "=" +
                            user_password + "&" + login_submit_info;
      CookieContainer container_cookie = new CookieContainer();
      HttpWebRequest web_request;

      web_request = (HttpWebRequest)WebRequest.Create(
          "http://www.example_url.com/login_page/");  // or insert the `url` string that contains
                                                      // the valid website URL
      web_request.CookieContainer = container_cookie;
      web_request.Method = post_method;  // for web request
      web_request.ContentType = type_webcontent;
      web_request.KeepAlive = true;

      using (Stream web_stream_request = web_request.GetRequestStream())

          // generate a proper web request
          using (StreamWriter writer = new StreamWriter(web_stream_request)) {
        writer.Write(string_login, user_name, user_password);
      }

      using (var web_stream_response = web_request.GetResponse().GetResponseStream()) using (
          var web_response_reader = new StreamReader(web_stream_response)) {
        var user_check = web_response_reader.ReadToEnd();
        Console.WriteLine(user_check);  // the result
      }

      MessageBox.Show("Successful login to website!");
    }
  }
}

Successful login to website!

// Install `Selenium.WebDriver` NuGet Package
// Install `Selenium.WebDriver.ChromeDriver` NuGet Package

using System;
using System.Windows.Forms;
using System.Net;
// using System.Net.Http;
using System.IO;
// using System.Collections.Specialized;

using OpenQA.Selenium;
using OpenQA.Selenium.Chrome;
using OpenQA.Selenium.Support.UI;

namespace login_website {
  public partial class Form1 : Form {
    public Form1() {
      InitializeComponent();
    }
    private void button1_Click(object sender, EventArgs e) {
      // run selenium | starts from...
      ChromeDriver chrome_driver = new ChromeDriver(
          @"chromedriver_win32");  // install the selenium chrome web driver for `ChromeDriver`
      chrome_driver.Url = @"https://fif.com/login";
      chrome_driver.Navigate();
      IWebElement web_element = chrome_driver.FindElementById(
          "user_name");  // install selenium web driver to use `FindElementById()` method
      web_element.SendKeys("...");
      web_element = chrome_driver.FindElementById("user_password");
      web_element.SendKeys("...");
      web_element = chrome_driver.FindElementByXPath(
          @"//*[@id=""main""]/div/div/div[2]/table/tbody/tr/td[1]/div/form/fieldset/table/tbody/tr[6]/td/button");
      web_element.Click();

      CookieContainer cookie_container = new CookieContainer();

      // get the cookies from the website
      foreach (OpenQA.Selenium.Cookie web_cookie in chrome_driver.Manage().Cookies.AllCookies) {
        string user_name = web_cookie.Name;
        string user_value = web_cookie.Value;
        cookie_container.Add(
            new System.Net.Cookie(user_name, user_value, web_cookie.Path, web_cookie.Domain));
      }

      // generate a proper web request
      HttpWebRequest http_web_request = (HttpWebRequest)HttpWebRequest.Create(
          "https://example.com/web_content/com_example/web_tools/page_capacity/login_values/");  // or something like "https://fif.com/components/com_fif/tools/capacity/values/"
      http_web_request.CookieContainer = cookie_container;
      http_web_request.Method = "POST";
      http_web_request.ContentType = "application/x-www-form-urlencoded";

      StreamWriter stream_writer = new StreamWriter(http_web_request.GetRequestStream());
      stream_writer.Write("feeds=35");
      stream_writer.Close();

      WebResponse web_response = http_web_request.GetResponse();
      string response_imp =
          new System.IO.StreamReader(web_response.GetResponseStream()).ReadToEnd();
    }
  }
}

[redirect the user to the `index.php` after a successful login]

* or

[shows an error for wrong username or password for invalid user]

// try not to change the entry point of this C# code
// it's important to remember that the `website_login.Program.Main` in your C# project is the entry
// point of this C# program. changing the entry point can lead to many difficulties and logical or
// syntax errors

using System;
using System.Net;
using System.IO;

namespace website_login {
  public class Program {
    public static void Main(string[] args) {
      var add_primary = new Uri("https://www.example_website.com/");
      var container_cookie = new CookieContainer();  // for web request

      // generate a proper web request | special HTTP implementation of the `WebRequest` class
      HttpWebRequest post_request_web =
          (HttpWebRequest)HttpWebRequest.Create("https://www.example_website.com/");
      post_request_web.CookieContainer = container_cookie;

      /*
       * setting the agent (user_agent) and accepting the header values
       * these are important to simulate a real web browser
       */
      post_request_web.UserAgent =
          "Chrome/5.3 (Windows Professional 11.2; WOW32) Chrome/45.0.2454.101";  // change it with
                                                                                 // respect to your
                                                                                 // platform, OS,
                                                                                 // and browser
      post_request_web.Accept =
          "text_type/html,c_sharp_application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";  // set values

      Console.WriteLine("[response from the server...]");
      Console.WriteLine();

      // generate a proper web response
      using (WebResponse get_response_web = post_request_web.GetResponse()) {
        // to read the response from the web server
        using (StreamReader stream_reader =
                   new StreamReader(get_response_web.GetResponseStream())) {
          Console.WriteLine(stream_reader.ReadToEnd());  // display
        }
      }

      post_request_web = (HttpWebRequest)HttpWebRequest.Create("https://www.example_website.com/");

      // setting `container_cookie` as a cookie container object
      post_request_web.CookieContainer = container_cookie;

      post_request_web.UserAgent =
          "Chrome/5.3 (Windows Professional 11.2; WOW32) Chrome/45.0.2454.101";  // change it with
                                                                                 // respect to your
                                                                                 // platform, OS,
                                                                                 // and browser
      post_request_web.Accept =
          "text_type/html,c_sharp_application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";  // set values

      post_request_web.Method = "POST";  // POST method because of web request
      post_request_web.ContentType =
          "application/x-www-form-urlencoded";  // it is a standard content type

      // the `user_infomration` variable contains the username and password of a user for login
      string user_information =
          string.Format("username={0}&password={1}", "your_username", "your_password");

      // encode the user information to send it to the web server
      byte[] _web_bytes = System.Text.Encoding.UTF8.GetBytes(user_information);

      post_request_web.ContentLength = _web_bytes.Length;

      using (Stream web_stream_user_info = post_request_web.GetRequestStream()) {
        web_stream_user_info.Write(_web_bytes, 0, _web_bytes.Length);
        web_stream_user_info.Close();
      }

      Console.WriteLine("[response form the server on user login...]");
      Console.WriteLine();

      using (WebResponse web_response_dll = post_request_web.GetResponse()) {
        // to read the response from the web server
        using (StreamReader stream_reader_dll =
                   new StreamReader(web_response_dll.GetResponseStream())) {
          Console.WriteLine(stream_reader_dll.ReadToEnd());  // display
        }
      }

      //....
    }
  }
}

[response from the server...]

... // some response from the website
*response from the `streamreader`*

[response from the server on user login...]
// response from the server or website after the first login attempt