Creates, decodes and verifies Blossm tokens. decode returns { headers, claims } and does not establish authenticity. validate verifies the signature, configured algorithm, audience and time bounds before returning claims. Tokens must have exactly three nonempty, canonical base64url segments; malformed encoding is rejected before calling the verifier.

The existing wire format uses ISO date strings for exp, nbf and iat, with expiresIn and activeIn expressed in milliseconds. Validation requires a parseable string exp, accepts an optional parseable string nbf, and rejects at the exact expiration instant. Missing or malformed expiry is rejected. Numeric JWT dates are not accepted as legacy dates. Audience arrays are currently encoded as a comma-separated string. Signing and verification callbacks own the signature bytes; the existing KMS integration uses DER ECDSA bytes. This is a legacy Blossm format rather than complete JOSE interoperability. Any change to standard JWT representation must update issuance, authentication, cache readers and cookie expiry together.