private static Map<String, Parameters> namedParameters() throws GeneralSecurityException {
    Map<String, Parameters> result = new HashMap<>();
    result.put("HKDF_SHA256", PredefinedPrfParameters.HKDF_SHA256);
    return Collections.unmodifiableMap(result);
  }
This key manager generates new {@code HkdfPrfKey} keys and produces new instances of {@code
HkdfStreamingPrf} and {@code HkdfPrf}.
java_src/src/main/java/com/google/crypto/tink/prf/HkdfPrfKeyManager.java