src/Http/HttpIntegration.php
protected function headers(array $server)
    {
        $headers = array();

        foreach ((array) $server as $key => $value) {
            $http = strpos($key, 'HTTP_') === 0;

            $string = strtolower(substr($key, 5));

            $string = str_replace('_', ' ', $string);

            $string = ucwords(strtolower($string));

            $key = str_replace(' ', '-', $string);

            $http && $headers[$key] = $value;
        }

        return $headers;
    }
protected function headers(array $server)
    {
        $headers = array();

        foreach ((array) $server as $key => $value) {
            $http = strpos($key, 'HTTP_') === 0;

            $string = strtolower(substr($key, 5));

            $string = str_replace('_', ' ', $string);

            $string = ucwords(strtolower($string));

            $key = str_replace(' ', '-', $string);

            $http && $headers[$key] = $value;
        }

        return $headers;
    }
Converts $_SERVER parameters to message header values.

@param  array $server
@return array