@AccessesPartialKey
  static HmacKey createHmacKeyFromRandomness(
      HmacParameters parameters,
      InputStream stream,
      @Nullable Integer idRequirement,
      SecretKeyAccess access)
      throws GeneralSecurityException {
    return HmacKey.builder()
        .setParameters(parameters)
        .setKeyBytes(Util.readIntoSecretBytes(stream, parameters.getKeySizeBytes(), access))
        .setIdRequirement(idRequirement)
        .build();
  }
This key manager generates new {@code HmacKey} keys and produces new instances of {@code
PrfHmacJce}.
java_src/src/main/java/com/google/crypto/tink/mac/HmacKeyManager.java