Proxy 407 Errors from External DTDs and XML Resources

Trace an unexpected 407 during document conversion to external DTDs, schemas or other resources opened by the parser.

A local document can still cause 407 during conversion. Its XML may name a DTD, schema or entity, and a renderer may fetch styles or images. The failing client can be inside that parser, after the original download finished.

Keep the exception stack and requested URI, then match it to input declarations or resource references. A standards-host DTD request is another operation from the page request. HTML-to-PDF conversion can likewise fail while retrieving remote assets.

For a .NET XmlReader input whose contract forbids DTDs and external resolution, use:

var settings = new XmlReaderSettings
{
    DtdProcessing = DtdProcessing.Prohibit,
    XmlResolver = null
};

Pass those settings to the component actually parsing the document. DtdProcessing chooses how to handle a DTD; XmlResolver controls external access. Prohibit rejects a document with a DTD—it does not strip the declaration. If the workflow requires one, choose approved local resolution or an explicitly routed resolver instead.

Keep defaults tied to the API/runtime. XmlReaderSettings uses Prohibit by default, and its default resolver changed to null starting in .NET Framework 4.5.2. A third-party converter can override them or use another parser.

Changing an XHTML declaration to an HTML doctype may affect one converter but does not configure its proxy. Establish required resources and their loader policy; authentication on the initial page client does not authenticate this second client.

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