// trust between the target audiences.
  repeated string audiences = 1;

  // ExpirationSeconds is the requested duration of validity of the request. The
  // token issuer may return a token with a different validity duration so a
  // client needs to check the 'expiration' field in a response.
  // +optional
  optional int64 expirationSeconds = 4;

  // BoundObjectRef is a reference to an object that the token will be bound to.

  //   3. Signer whose configured minimum is longer than the requested duration
  //
  // The minimum valid value for expirationSeconds is 600, i.e. 10 minutes.
  //
  // +optional
  optional int32 expirationSeconds = 8;

  // allowedUsages specifies a set of usage contexts the key will be
  // valid for.
  // See:
  // 	https://tools.ietf.org/html/rfc5280#section-4.2.1.3