@AccessesPartialKey
  static RsaSsaPkcs1PrivateKey toRsaSsaPkcs1PrivateKey(JwtRsaSsaPkcs1PrivateKey privateKey)
      throws GeneralSecurityException {
    RsaSsaPkcs1PublicKey publicKey =
        JwtRsaSsaPkcs1VerifyKeyManager.toRsaSsaPkcs1PublicKey(privateKey.getPublicKey());
    return RsaSsaPkcs1PrivateKey.builder()
        .setPublicKey(publicKey)
        .setPrimes(privateKey.getPrimeP(), privateKey.getPrimeQ())
        .setPrivateExponent(privateKey.getPrivateExponent())
        .setPrimeExponents(privateKey.getPrimeExponentP(), privateKey.getPrimeExponentQ())
        .setCrtCoefficient(privateKey.getCrtCoefficient())
        .build();
  }
This key manager generates new {@code JwtRsaSsaPkcs1PrivateKey} keys and produces new instances
of {@code JwtPublicKeySign}.
java_src/src/main/java/com/google/crypto/tink/jwt/JwtRsaSsaPkcs1SignKeyManager.java