@AccessesPartialKey
  private static HmacPrfKey newKey(HmacPrfParameters parameters, @Nullable Integer idRequirement)
      throws GeneralSecurityException {
    if (idRequirement != null) {
      throw new GeneralSecurityException("Id Requirement is not supported for HMAC PRF keys");
    }
    return HmacPrfKey.builder()
        .setParameters(parameters)
        .setKeyBytes(SecretBytes.randomBytes(parameters.getKeySizeBytes()))
        .build();
  }
This key manager generates new {@code HmacPrfKey} keys and produces new instances of {@code
PrfHmacJce}.
java_src/src/main/java/com/google/crypto/tink/prf/HmacPrfKeyManager.java