How should a Spring Security resource server validate JWTs?

Uses Resource Server and JwtDecoder to validate signature, issuer, audience, time, algorithms, key rotation, and authority mapping.

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TL;DR

I configure Spring Security as an OAuth2 Resource Server with a trusted issuer or an explicit JWK set and a JwtDecoder. The decoder verifies the signature with an allowed algorithm and key, then validates time claims such as expiry and not-before plus the expected issuer. I also validate that the audience identifies this API. A converter maps trusted scopes or claims into authorities, and failed validation produces an authentication failure before controller code runs.

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JwtDecoder, JWK discovery, signature trust, issuer and audience, timestamps, algorithms, claims, and failure handling.

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Core answer
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Overview
Parsing claims is not authentication; the decoder must prove that a trusted issuer created a token for this API.
I configure Spring Security as an OAuth2 Resource Server with a trusted issuer or an explicit JWK set and a JwtDecoder. The decoder verifies the signature with an allowed algorithm and key, then validates time claims such as expiry and not-before plus the expected issuer. I also validate that the audience identifies this API. A converter maps trusted scopes or claims into authorities, and failed validation produces an authentication failure before controller code runs.
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The token header cannot choose an arbitrary trusted algorithm or key source. JWK retrieval, caching, rotation, clock skew, and authorization-server availability need deliberate configuration and monitoring. A valid signature does not make every claim suitable for authorization: claim names, types, issuer ownership, and mapping rules matter. Spring's default scope mapping commonly creates authorities, but custom role claims require an explicit converter and tests.

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Only base64-decoding the JWT.
Skipping audience validation.
Trusting arbitrary role claims without issuer mapping.

How should a Spring Security resource server validate JWTs?

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