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Coinbase Api Java POST request “Invalid Signature”

Posted by: admin August 10, 2018 Leave a comment


I am trying to send a POST request to the coinbase sandbox endpoint. When signing the request I always get an “Invalid Signature” response. It seems that coinbase requires the JSON message be base 64 encoded and sent as a part of the signature. I am fairly new to POST requests and have never signed a message before. Can someone please let me know what I am doing wrong. I have been stuck on this issue for a week so any input is much appreciated.

The relevant part of my code is below

public void postOrder() throws InvalidKeyException, NoSuchAlgorithmException, CloneNotSupportedException, ClientProtocolException, IOException {

    String message = "{ \n"+
               " \"size\":\"1.00\", \n"+
               " \"price\":\"0.80\", \n"+
               " \"side\":\"buy\", \n"+
               " \"product_id\":\"BTC-USD\" \n"+

    JSONObject json = new JSONObject(message);
    message = json.toString();
            String timestamp= Instant.now().getEpochSecond()+"";
            String accessSign = getAccess(timestamp,"POST","/orders",message);
            String apiKey = properties.getProperty("key");
            String passphrase = properties.getProperty("passphrase");

            URL url = new URL("https://api-public.sandbox.pro.coinbase.com/orders");
            HttpURLConnection connection = (HttpURLConnection)url.openConnection();
            connection.setRequestProperty("accept", "application/json");
            connection.setRequestProperty("content-type", "application/json; charset=UTF-8");
            connection.setRequestProperty("CB-ACCESS-KEY", apiKey);
            connection.setRequestProperty("CB-ACCESS-SIGN", accessSign);
            connection.setRequestProperty("CB-ACCESS-TIMESTAMP", timestamp);
            connection.setRequestProperty("CB-ACCESS-PASSPHRASE", passphrase);
            connection.setRequestProperty("User-Agent", "Java Client"); 

          try { 
            OutputStream output = connection.getOutputStream(); 
          } catch (Exception e) {

          String status = connection.getResponseMessage();
            System.out.println("STATUS: "+status);  

     }catch(Exception e) {

 private String getAccess(String timestamp, String method, String path, String param) throws NoSuchAlgorithmException, InvalidKeyException, CloneNotSupportedException, IllegalStateException, UnsupportedEncodingException {

        String secretKeyString = properties.getProperty("secret");

        String prehash = timestamp+method+path+param;
        byte[] secretKeyDecoded = Base64.getDecoder().decode(secretKeyString);
        SecretKey secretKey = new SecretKeySpec(secretKeyDecoded, "HmacSHA256");
        Mac hmacSha256 = Mac.getInstance("HmacSHA256");

        return Base64.getEncoder().encodeToString(hmacSha256.doFinal(prehash.getBytes()));