Send email using the GMail SMTP server from a PHP page

I am trying to send an email via GMail's SMTP server from a PHP page, but I get this error:

authentication failure [SMTP: SMTP server does no support authentication (code: 250, response: mx.google.com at your service, [98.117.99.235] SIZE 35651584 8BITMIME STARTTLS ENHANCEDSTATUSCODES PIPELINING)]

Can anyone help? Here is my code:

<?php
require_once "Mail.php";

$from = "Sandra Sender <[email protected]>";
$to = "Ramona Recipient <[email protected]>";
$subject = "Hi!";
$body = "Hi,\n\nHow are you?";

$host = "smtp.gmail.com";
$port = "587";
$username = "[email protected]";
$password = "testtest";

$headers = array ('From' => $from,
  'To' => $to,
  'Subject' => $subject);
$smtp = Mail::factory('smtp',
  array ('host' => $host,
    'port' => $port,
    'auth' => true,
    'username' => $username,
    'password' => $password));

$mail = $smtp->send($to, $headers, $body);

if (PEAR::isError($mail)) {
  echo("<p>" . $mail->getMessage() . "</p>");
 } else {
  echo("<p>Message successfully sent!</p>");
 }
?>

// Pear Mail Library
require_once "Mail.php";

$from = '<[email protected]>';
$to = '<[email protected]>';
$subject = 'Hi!';
$body = "Hi,\n\nHow are you?";

$headers = array(
    'From' => $from,
    'To' => $to,
    'Subject' => $subject
);

$smtp = Mail::factory('smtp', array(
        'host' => 'ssl://smtp.gmail.com',
        'port' => '465',
        'auth' => true,
        'username' => '[email protected]',
        'password' => 'passwordxxx'
    ));

$mail = $smtp->send($to, $headers, $body);

if (PEAR::isError($mail)) {
    echo('<p>' . $mail->getMessage() . '</p>');
} else {
    echo('<p>Message successfully sent!</p>');
}

Using Swift mailer, it is quite easy to send a mail through Gmail credentials:

<?php
require_once 'swift/lib/swift_required.php';

$transport = Swift_SmtpTransport::newInstance('smtp.gmail.com', 465, "ssl")
  ->setUsername('GMAIL_USERNAME')
  ->setPassword('GMAIL_PASSWORD');

$mailer = Swift_Mailer::newInstance($transport);

$message = Swift_Message::newInstance('Test Subject')
  ->setFrom(array('[email protected]' => 'ABC'))
  ->setTo(array('[email protected]'))
  ->setBody('This is a test mail.');

$result = $mailer->send($message);
?>