src/Services/ApiService.php
public function getAuthorizationHeader($apiKey="")
    {
        if (empty($apiKey)) {
            if (empty($this->_apiKey)) throw new GreenhouseServiceException('No key provided to encode.');
            $apiKey = $this->_apiKey;
        }
        $key = rtrim($apiKey, ':') . ':';
        
        return 'Basic ' . base64_encode($key);
    }
public function getAuthorizationHeader($apiKey="")
    {
        if (empty($apiKey)) {
            if (empty($this->_apiKey)) throw new GreenhouseServiceException('No key provided to encode.');
            $apiKey = $this->_apiKey;
        }
        $key = rtrim($apiKey, ':') . ':';
        
        return 'Basic ' . base64_encode($key);
    }
Base64 Encode an API key.  Greenhouse's encoding treats the key as the username with
a blank password.  Here we append the : for convenience.  We also handle the case
where the user appends the : themselves.  If no key is provided, we will attempt
to encode the private api key property.

@params  string  $apiKey     A greenhouse job board API key.
@return  string  The other side of an Authorization header (Basic: <encoded key>)