unique
  raw: {"sub":"alpha","exp":2000000000}
  default: {"sub":"alpha","exp":2000000000}
  policy: accepted by this duplicate-key check
repeated subject
  raw: {"sub":"alpha","sub":"beta"}
  default: {"sub":"beta"}
  policy: duplicate key: sub
repeated expiry
  raw: {"exp":100,"exp":2000000000}
  default: {"exp":2000000000}
  policy: duplicate key: exp
escaped name
  raw: {"sub":"alpha","\u0073ub":"beta"}
  default: {"sub":"beta"}
  policy: duplicate key: sub
different case
  raw: {"sub":"alpha","SUB":"beta"}
  default: {"sub":"alpha","SUB":"beta"}
  policy: accepted by this duplicate-key check
nested repeat
  raw: {"profile":{"label":"a","label":"b"}}
  default: {"profile":{"label":"b"}}
  policy: duplicate key: label
separate objects
  raw: {"left":{"label":"a"},"right":{"label":"b"}}
  default: {"left":{"label":"a"},"right":{"label":"b"}}
  policy: accepted by this duplicate-key check
PASS: 7 fixtures; raw payload, synthetic HMAC, default parse and duplicate policy match.
Fixture integrity only: issuer, audience, time and application authorization are not validated.