How to use

sign

method

in

com.google.auth.oauth2.ServiceAccountJwtAccessCredentials

@Test
public void sign_sameAs()
  throws IOException, NoSuchAlgorithmException, InvalidKeyException, SignatureException {
 PrivateKey privateKey = ServiceAccountCredentials.privateKeyFromPkcs8(SA_PRIVATE_KEY_PKCS8);
 byte[] toSign = {0xD, 0xE, 0xA, 0xD};
 ServiceAccountJwtAccessCredentials credentials = ServiceAccountJwtAccessCredentials.newBuilder()
   .setClientId(SA_CLIENT_ID)
   .setClientEmail(SA_CLIENT_EMAIL)
   .setPrivateKey(privateKey)
   .setPrivateKeyId(SA_PRIVATE_KEY_ID)
   .build();
 byte[] signedBytes = credentials.sign(toSign);
 Signature signature = Signature.getInstance(OAuth2Utils.SIGNATURE_ALGORITHM);
 signature.initSign(credentials.getPrivateKey());
 signature.update(toSign);
 assertArrayEquals(signature.sign(), signedBytes);
}