// Defaulted to nil.
  // +optional
  optional bool immutable = 5;

  // Data contains the secret data. Each key must consist of alphanumeric
  // characters, '-', '_' or '.'. The serialized form of the secret data is a
  // base64 encoded string, representing the arbitrary (possibly non-string)
  // data value here. Described in https://tools.ietf.org/html/rfc4648#section-4
  // +optional