# Challenge Sometimes, Apps may want to validate an account by asking it to sign a predefined text string (challenge) with one of its keys. It can be useful for a front-end/back-end solution. The **APP** front-end ask the **PKSA** to sign a message with the account's key, then send it to its back-end with requests related to the account. The back-end can then validate the signed challenge against the account public key. --- # 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://docs.hiveauth.com/developer-documentation/has-for-applications/challenge.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.