(mongodb >=1.15.0)
MongoDB\Driver\ClientEncryption::getKeyByAltName — Gets a key document by an alternate name
$keyAltName): ?object
   Finds a single key document in the key vault collection with the given
   alternate name keyAltName.
  
keyAltNameAlternate name for the key document.
   Returns the key document, or null if no document matched.