Hi friends,
If you are using PDO in php , Now you can Authenticate user using simple code.

include 'conn.php';
try
{
    $username = $_POST['user'];
    $password = $_POST['pass'];
        $smt=$conn->prepare("SELECT * FROM signup WHERE username = '".$username."'");
        $smt->execute();
        $result=$smt->fetch(PDO::FETCH_OBJ);
        $prev=$result->Password;
        $usr=$result->Username;
           if(password_verify($password,$prev)& $username===$usr)
        {
        // Set username session variable
        $_SESSION['user'] = $username;
        // Jump to secured page
        header('location:index.php');
        exit;
    }
    else
    {
        $_SESSION['login-error']="Incorrect username or password";
        header('location:signin.php');
        exit;
    }
}