# Extensions The mechanism for generating public key credentials, as well as requesting and generating Authentication assertions, can be extended to suit particular use cases. Each case is addressed by defining a registration extension. Standard extensions are usually listed in the dedicated IANA Registry available at {% hint style="warning" %} This library is ready to handle extension inputs and outputs, but no concrete implementations are provided, except for the `appip` extension. It is up to you, depending on the extensions you want to support, to create the extension handlers. {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://webauthn-doc.spomky-labs.com/v4.5/webauthn-in-a-nutshell/extensions.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.