How to post form login using jsoup?

Question 1

The URL that are you using in order to do the POST request is wrong, simply because when you have to do a specific request to a form you should use the web page that is present in the form tag, in this case "authentication.php".

So the code will be:

    package jsouptest;

    import org.jsoup.Connection;
    import org.jsoup.Jsoup;
    import org.jsoup.nodes.Document;

    public class JsouptTest {
        public static void main(String[] args) throws Exception {

           Connection.Response loginForm = Jsoup.connect("https://www.desco.org.bd/ebill/login.php")
            .method(Connection.Method.GET)
            .execute();

           Document document = Jsoup.connect("https://www.desco.org.bd/ebill/authentication.php")
            .data("cookieexists", "false")
            .data("username", "32007702")
            .data("login", "Login")
            .cookies(loginForm.cookies())
            .post();
           System.out.println(document);

       }

    }

This one correctly retrieves the web page that you want.

Question 2

For me the problem was that I didn't send the viewstate, eventvalidation, viewstategenerator values.

To get these values you have to first send a GET request to the login form page. In my instance this was a default.aspx page.

Then you have to extract those values and put them into variables. Also of course you need the form login and password field ids, the submit button's id, among other things. For a list of all those variable that are sent, login manually and use chrome dev tools (inspect elements) to look at the network tab for a POST request. Inside it should show the username and password you submitted. There you will see other variables that are sent.

network tab in dev tools example

Next, send a POST request including all those variables, save the cookies from the response into a variable, and you can then use that to go to another page.

Code:

import java.io.IOException;
import java.util.Map;
import org.jsoup.Connection;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.nodes.FormElement;


public class get_example {

public static void main(String[] args) throws IOException {
    //===================================
    Connection.Response response2 = Jsoup.connect("yourloginpage")
            .method(Connection.Method.GET)
            .execute();

    Document responseDocument = response2.parse();

    Element eventValidation = responseDocument.select("input[name=__EVENTVALIDATION]").first();
    Element viewState = responseDocument.select("input[name=__VIEWSTATE]").first();
    Element viewStateGen = responseDocument.select("input[name=__VIEWSTATEGENERATOR]").first();



    Connection.Response response = Jsoup.connect("yourloginpage")
            .method(Connection.Method.POST)
            .data("ctl00$plnMain$txtLogin", "username")
            .data("ctl00$plnMain$txtPassword", "password")
            .data("ctl00$plnMain$Submit1", "Log In")
            .data("ctl00$ucCopyright$hdnPrivacyStatement", "Privacy Statement")
            .data("ctl00$ucCopyright$hdnTermsOfUse", "Terms of Use")
            .data("__VIEWSTATE", viewState.attr("value"))
            .data("__VIEWSTATEGENERATOR", viewStateGen.attr("value"))
            .data("__EVENTVALIDATION", eventValidation.attr("value"))
            .execute();


    Map<String, String> cookies = response.cookies();


    Document homePage = Jsoup.connect("anotherpage")
            .cookies(cookies)
            .get();


    System.out.println(homePage.body().html());

}
}

Question 3

In my case, it consists in three steps:

Get cookies from login form page;
Post credentials to login form action= URL, renew cookies;
The user will be redirected to index page. Don't parse here, just send Response to the final target URL.
Parse when you reach the final page.

The cookies should be renewed in every step, sometimes add entries, and sometimes you must clear it and reset. Be sure to check the network transmission with Internet Explorer/Chrome/Firefox Dev tool (F12), in the Network panel, cookies part.