sfcontact.php

<?php

function getHashedId($id) {
  $random = base64_encode(random_bytes(32));
  $stringToSign = $id . "\0" . $random;
  $hash = hash('sha256', $stringToSign);
  return base64_encode($hash . "\0" . $random);
}

function verifyHashedId($id, $hashedId) {
  $a = explode("\0", base64_decode($hashedId));
  $hash = $a[0];
  $random = $a[1];
  $stringToSign = $id . "\0" . $random;
  return hash('sha256', $stringToSign) === $hash;
}

function getContactId($contact, $hashedId) {
  foreach ($contact as $c) {
    if (verifyHashedId($c['Id'], $hashedId)) {
      return $c['Id'];
    }
  }
  return null;
}

function getContactLink($c) {
  $content = $c['Email']."\0".getHashedId($id)."\0".time()."\0".base64_encode(random_bytes(32));
  $contentSigned = $content."\n". hash_hmac('sha256',$content,getenv('SECRET'));          
  return base64_encode($contentSigned);
}

function generateTmpLinks($contact) {
  $links = array();
  foreach ($contact as $c) {
    $links[] = getContactLink($c);
  }
  return $links;
}