src/Web/ResponseBuilder.php
protected function getHeadersPrepared() {
        $cookiesData = $this->getCookiesPrepared();
        foreach ($cookiesData as $cookieStr) {
            $this->headers->add('Set-Cookie', $cookieStr);
        }
        $headersArray = [];
        if ($this->_headers) {
            foreach ($this->getHeaders() as $name => $values) {
                $name = str_replace(' ', '-', ucwords(str_replace('-', ' ', $name)));
                if (!isset($headersArray[$name])) {
                    $headersArray[$name] = [];
                }
                foreach ($values as $value) {
                    $headersArray[$name][] = $value;
                }
            }
        }
        return $headersArray;
    }
protected function getHeadersPrepared() {
        $cookiesData = $this->getCookiesPrepared();
        foreach ($cookiesData as $cookieStr) {
            $this->headers->add('Set-Cookie', $cookieStr);
        }
        $headersArray = [];
        if ($this->_headers) {
            foreach ($this->getHeaders() as $name => $values) {
                $name = str_replace(' ', '-', ucwords(str_replace('-', ' ', $name)));
                if (!isset($headersArray[$name])) {
                    $headersArray[$name] = [];
                }
                foreach ($values as $value) {
                    $headersArray[$name][] = $value;
                }
            }
        }
        return $headersArray;
    }
Get prepared headers array
@return array
@throws InvalidConfigException