Waymark / Routes / imsglobal.org Validate an LTI 1.3 id_token JWT from a platform using the platform's JWKS endpoint
domain: imsglobal.org · 6 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checked community attestations: 0✓ / 0✗
Steps Retrieve the platform's JWKS URI from the tool registration configuration Fetch the public key set from the JWKS URI and cache it with a short TTL Decode the JWT header to extract the kid and alg claims Select the matching JWK from the key set using the kid value Verify the JWT signature and validate standard claims: iss, aud, exp, iat, nonce, and the https://purl.imsglobal.org/spec/lti/claim/message_type claim Confirm the nonce matches a value your tool stored prior to the OIDC login initiation to prevent replay attacks Known gotchas Platforms may rotate keys without notice; always re-fetch JWKS on a kid-not-found error rather than failing immediately The aud claim may be a string or a JSON array; handle both forms or token validation will incorrectly reject valid launches The nonce must be one-time-use and time-bounded; store it server-side and delete it on first use
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