@AccessesPartialKey
  private static JwtMac createFullJwtHmac(JwtHmacKey key) throws GeneralSecurityException {
    validate(key.getParameters());
    HmacKey hmacKey =
        HmacKey.builder()
            .setParameters(
                HmacParameters.builder()
                    .setKeySizeBytes(key.getParameters().getKeySizeBytes())
                    .setHashType(getHmacHashType(key.getParameters().getAlgorithm()))
                    .setTagSizeBytes(getTagLength(key.getParameters().getAlgorithm()))
                    .build())
            .setKeyBytes(key.getKeyBytes())
            .build();
    return new JwtHmac(PrfMac.create(hmacKey), key);
  }
This key manager generates new {@code JwtHmacKey} keys and produces new instances of {@link
JwtHmac}.
java_src/src/main/java/com/google/crypto/tink/jwt/JwtHmacKeyManager.java