JWKS Endpoint Returns 404: How to Diagnose and Fix It

Every day, over 600 million identity attacks target Microsoft properties, and almost every defense mechanism relies on validating a JSON Web Token (JWT) signature against a public key fetched from a JSON Web Key Set (JWKS) endpoint. A common issue arises when the JWKS endpoint returns a 404 error, which often indicates a misconfiguration rather than the Identity Provider (IdP) being down. The text outlines the common root causes for this error, such as incorrect discovery documents, wrong issuer URLs, and environment mix-ups, and provides diagnostic steps and solutions to resolve these issues swiftly. It emphasizes the importance of correctly parsing discovery documents to obtain the jwks_uri and configuring systems to handle multi-tenant issuer URLs properly. Additionally, caching strategies for JWKS responses in Node.js and Python are discussed, underscoring the need to follow RFC guidelines to ensure key rotation is handled properly. The document offers practical debugging insights and highlights the role of Content Delivery Networks (CDNs) in potentially masking the real status of JWKS endpoints, urging practitioners to investigate cache headers and CDN settings when facing 404 errors.

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