@Test public void sign_sameAs() throws IOException, NoSuchAlgorithmException, InvalidKeyException, SignatureException { byte[] toSign = {0xD, 0xE, 0xA, 0xD}; ServiceAccountCredentials credentials = ServiceAccountCredentials.fromPkcs8( SA_CLIENT_ID, SA_CLIENT_EMAIL, SA_PRIVATE_KEY_PKCS8, SA_PRIVATE_KEY_ID, null); byte[] signedBytes = credentials.sign(toSign); Signature signature = Signature.getInstance(OAuth2Utils.SIGNATURE_ALGORITHM); signature.initSign(credentials.getPrivateKey()); signature.update(toSign); assertArrayEquals(signature.sign(), signedBytes); }