@Override
  @Nullable
  public Integer getIdRequirementOrNull() {
    return idRequirement;
  }
Represents the Aead XChaCha20-Poly1305 proposed in the RFC draft at
https://datatracker.ietf.org/doc/html/draft-arciszewski-xchacha-03.

<p>XChaCha20-Poly1305 allows no parameters; hence the main part here is really just the key
material. However, Tink allows prefixing every ciphertext with an ID-dependent prefix, see {@link
XChaCha20Poly1305Parameters.Variant}.
java_src/src/main/java/com/google/crypto/tink/aead/XChaCha20Poly1305Key.java