private function mergeHeaders() {

        // Initialize the merged headers.
        $mergedHeaders = [];

        // Handle each header.
        foreach (array_merge($this->getConfiguration()->getHeaders(), $this->getHeaders()) as $key => $value) {
            $mergedHeaders[] = implode(": ", [$key, $value]);
        }

        // Return the merged headers.
        return $mergedHeaders;
    }