src/Auth/AuthAbstract.php
public function getHeaders($key = null)
    {
        if ($key === null) {
            return $this->headers;
        }

        if (isset($this->headers[$key])) {
            return $this->headers[$key];
        }

        return false;
    }
public function getHeaders($key = null)
    {
        if ($key === null) {
            return $this->headers;
        }

        if (isset($this->headers[$key])) {
            return $this->headers[$key];
        }

        return false;
    }
Get response headers

@param null $key
@return array|string|false