Login to different accounts viz. yahoo/gmail/facebook

Question

I have a problem:

1. take username and password from user from text filed.
2. Automatically sign in to yahoo/google/facebook account and display the webpage in webview.

Basically I dont want user to directly put username and password to yahoo account but go through my application.

Here is my code:

String login = "abcd";
String pwd = "1234";
String streamSend = "";
Object pwfields;
      //initial post to login handler
 URL url1;
 PrintStream outStream;
 HttpURLConnection conn;
        try {
            url1 = new URL("https://login.yahoo.com/config/login?");

        conn = (HttpURLConnection)url1.openConnection();
        conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
        conn.setDoOutput(true);
        conn.setDoInput(true);
        conn.setRequestMethod("POST");
        //generate request stream
        outStream = new PrintStream(conn.getOutputStream());


        //add the fields and values for each part of the multipart POST
        streamSend += "Content-Disposition: form-data; login=\""+login+"\"\r\n";
        streamSend += "\r\n";
        streamSend += pwd+"\r\n";

        //send POST to server and close stream
        outStream.print(streamSend);

 webView.loadUrl("https://login.yahoo.com/config/login?");
 webView.requestFocus();

This code have problems, it doesn't work..and also do I have to encrypt password. Any sample code or reference wud be very helpful.