loginUser.php

<?php
require_once "connection.php";
$con = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_DATABASE);
$username = $_POST["username"];
$password = $_POST["password"];
    $statement = mysqli_prepare($con, "SELECT * FROM users WHERE username = ? AND password = ?");
    mysqli_stmt_bind_param($statement, "ss", $username, $password);
    mysqli_stmt_execute($statement);
    mysqli_stmt_store_result($statement);
    mysqli_stmt_bind_result($statement, $user_id, $username, $password);
    $response = array();
    $response["Dados incorretos. Por favor tente de novo."] = false;
    while(mysqli_stmt_fetch($statement)){
        $response["Bem-vindo!"] = true;
      }
    echo json_encode($response);
?>