public static Prf create(HmacPrfKey key) throws GeneralSecurityException {
    return new PrfHmacJce(
        "HMAC" + key.getParameters().getHashType(),
        new SecretKeySpec(key.getKeyBytes().toByteArray(InsecureSecretKeyAccess.get()), "HMAC"));
  }
Given an HmacPrfKey, returns an instance of the Prf interface.
java_src/src/main/java/com/google/crypto/tink/subtle/PrfHmacJce.java