GuzzleHttpExceptionClientException: Client error: `POST     http://local.dev/entity/distribution_ingest/NGM:123456?_format=hal_json` resulted in a `401 Unauthorized` response: No authentication credentials provided. in GuzzleHttpExceptionRequestException::create() (line 107 of /home/vagrant/docroot/vendor/guzzlehttp/guzzle/src/Exception/RequestException.php).

$rest_response = $client->post($endpoint, [
  'auth' => ['admin', 'some_admin_password'], // IT ONLY WORKS WHEN THIS IS HERE.
  'body' => $some_serialized_body,
  'headers' => [
    'Content-Type' => 'application/hal+json',
    'X-CSRF-Token' => $token,
  ],
]);