	protected String getCorsDomain(String referer, String userAgent)
	{
		String dom = null;

		if (referer != null && referer.toLowerCase()
				.matches("https?://([a-z0-9,-]+[.])*draw[.]io/.*"))
		{
			dom = referer.toLowerCase().substring(0,
					referer.indexOf(".draw.io/") + 8);
		}
		else if (referer != null && referer.toLowerCase()
				.matches("https?://([a-z0-9,-]+[.])*diagrams[.]net/.*"))
		{
			dom = referer.toLowerCase().substring(0,
					referer.indexOf(".diagrams.net/") + 13);
		}
		else if (referer != null && referer.toLowerCase()
				.matches("https?://([a-z0-9,-]+[.])*quipelements[.]com/.*"))
		{
			dom = referer.toLowerCase().substring(0,
					referer.indexOf(".quipelements.com/") + 17);
		}
		// Enables Confluence/Jira proxy via referer or hardcoded user-agent (for old versions)
		// UA refers to old FF on macOS so low risk and fixes requests from existing servers
		else if ((referer != null
				&& referer.equals("draw.io Proxy Confluence Server"))
				|| (userAgent != null && userAgent.equals(
						"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:50.0) Gecko/20100101 Firefox/50.0")))
		{
			dom = "";
		}

		return dom;
	}
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.