How do I fetch login data from PHP script to my MainActivity?

This is my PHP script:

<?php
    error_reporting(E_ALL);
    ini_set('display_errors', 1);
    header('Access-Control-Allow-Origin: *');
    header('Access-Control-Allow-Methods: POST, GET, OPTIONS');

    $con=mysqli_connect($server,$username,$pass);
    $connection=mysqli_select_db($con,$database);

    $sql="SELECT * FROM `electric_database_users` WHERE 
    `User name/no`='".$_POST["username"]."' AND `Password`='".$_POST["password"]."'";
    $result = $con->query($sql);
    if ($result->num_rows > 0)
        echo "login found";
    else
        echo "Invalid login";

    $con->close();
 ?>

In javascript, I could fetch the data using $ajax call:

$.ajax({
    url: '/login_screen/backend.php',
    type: 'POST',
    data: { "input": "sign in",
          "username":  username,
          "password": password},
    success: function(response) {
        if(response=="login found")
            //Login successful
    },
    complete: function() {}
  });

Now I want to implement the same logic from my android app i.e., I want to fetch the login details from my backend.php. Is there something equivalent to $ajax call in android?

  empno=(EditText) findViewById(R.id.empno);
  pass=(EditText) findViewById(R.id.pass);
  login=(Button) findViewById(R.id.login);

  login.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

             //how do I proceed here?
        }
  });