About PHP implementation for AMP cache

Hello!
I’m really in trouble. How do I implement the following code in WordPress?

Where and how to edit in the code?
What file name and extension should I save?
Where should I save it?

function generateURL( $page ) {
$domain = ‘example.com’;
$url = $domain . $page;

$timestamp = time();
$ampBaseUrl = “https://” . str_replace( array( ‘-‘, ‘.’ ), array(‘–‘, ‘-‘ ), $domain ) . “.cdn.ampproject.org”;
$signatureUrl = ‘/update-cache/c/s/’ . $url . ‘?amp_action=flush&amp_ts=’ . $timestamp;

// opening the private key
$pkeyid = openssl_pkey_get_private( “file:///Users/boofoo/private-key.pem” );
if ( $pkeyid == false ) {
echo ‘could not open the private key.’;
exit;
}

// generating the signature
openssl_sign( $signatureUrl, $signature, $pkeyid, OPENSSL_ALGO_SHA256 );
openssl_free_key( $pkeyid );

// urlsafe base64 encoding
$signature = $this->urlsafe_b64encode( $signature );

// final url for updating
$ampUrl = $ampBaseUrl . $signatureUrl . “&amp_url_signature=” . $signature;

return $ampUrl;

}

function urlsafe_b64encode( $string ) {
return str_replace( array( ‘+’, ‘/’, ‘=’ ), array( ‘-‘, ‘_’, ” ), base64_encode( $string ) );
}