wp_filter_oembed_result

 *
 * Only filters 'rich' and 'video' response types.
 *
 * @since 4.4.0
 *
 * @param string $result The oEmbed HTML result.
 * @param object $data   A data object result from an oEmbed provider.
 * @param string $url    The URL of the content to be embedded.
 * @return string The filtered and sanitized oEmbed result.
 */
function wp_filter_oembed_result( $result, $data, $url ) {
	if ( false === $result || ! in_array( $data->type, array( 'rich', 'video' ), true ) ) {
		return $result;
	}

	$wp_oembed = _wp_oembed_get_object();

	// Don't modify the HTML for trusted providers.
	if ( false !== $wp_oembed->get_provider( $url, array( 'discover' => false ) ) ) {
		return $result;
	}

	$allowed_html = array(
		'a'          => array(
			'href' => true,
		),
		'blockquote' => array(),
		'iframe'     => array(
			'src'          => true,
			'width'        => true,
			'height'       => true,
			'frameborder'  => true,
			'marginwidth'  => true,
			'marginheight' => true,
			'scrolling'    => true,
			'title'        => true,
		),
	);

	$html = wp_kses( $result, $allowed_html );

	preg_match( '|(<blockquote>.*?</blockquote>)?.*(<iframe.*?></iframe>)|ms', $html, $content );
	// We require at least the iframe to exist.
	if ( empty( $content[2] ) ) {
		return false;
	}
	$html = $content[1] . $content[2];

	preg_match( '/ src=([\'"])(.*?)\1/', $html, $results );

	if ( ! empty( $results ) ) {
		$secret = wp_generate_password( 10, false );

		$url = esc_url( "{$results[2]}#?secret=$secret" );
		$q   = $results[1];

		$html = str_replace( $results[0], ' src=' . $q . $url . $q . ' data-secret=' . $q . $secret . $q, $html );
		$html = str_replace( '<blockquote', "<blockquote data-secret=\"$secret\"", $html );
	}

	$allowed_html['blockquote']['data-secret'] = true;
	$allowed_html['iframe']['data-secret']     = true;

	$html = wp_kses( $html, $allowed_html );