OKTA access token using token endpoint url returns http 401 error

Question

I am new to OKTA. Using the below code to get the access token.. but getting 401 unauthorized error in this line

inputBuff = new BufferedReader(new InputStreamReader(httpsClient.getInputStream()));

String oktaURL = "https://xxx.oktapreview.com/oauth2/default/v1/token";
            String urlParameters = “client_id=” + clientId+“grant_type=authorization_code&redirect_uri=”+“http://:8192/app”+"&code="+oktaCode;
            URL url1 = new URL(oktaURL);
            StringBuffer response = null;
            String output1;

            log.info("The url to get the access token:"+url1.toString());
            if (url1.getProtocol() != null && url1.getProtocol().startsWith("https")){
                
                //String encodedData = DatatypeConverter.printBase64Binary((clientId + ":" + clientSecret).getBytes("UTF-8"));
                //String authorizationHeaderString = "Authorization: Basic " + encodedData;
                
                httpsClient = (HttpsURLConnection) url1.openConnection();
                httpsClient.setRequestMethod("POST");
                httpsClient.setRequestProperty("Accept","application/json");    
                httpsClient.setRequestProperty("Authorization", "Basic " + Base64.getEncoder().encodeToString((clientId + ":" + clientSecret).getBytes()));
                httpsClient.setRequestProperty("Content-Type","application/x-www-form-urlencoded"); 
                httpsClient.setInstanceFollowRedirects(false);
                
                log.info ("Send the POST request");
                // Send post request
                httpsClient.setDoOutput(true);
                try (DataOutputStream opStream = new DataOutputStream(httpsClient.getOutputStream())) {                     
                    opStream.writeBytes(urlParameters);
                    opStream.flush();
                }
                
                inputBuff = new BufferedReader(new InputStreamReader(httpsClient.getInputStream())); // throwing 401 here.
                log.info("Read from the input stream");

                response = new StringBuffer();
                while ((output1 = inputBuff.readLine()) != null) {
                    response.append(output1);
                }
            }

            if (response != null) {
                String theString = response.toString();
                log.trace("Info:"+theString);
            }

I could navigate to OKTA server's login page via /authorize URL and then authentication is successful and coming back to my application. Now trying to get access token. Please help how to solve this in java.

I just checked the okta log, it says the below right above the authenticate success log.

Answer 1

Solve the issue, there were 2 issues.

1. Removed client_id from urlParameters as its given in Authorization header
2. Removed default from /token endpoint as its not give in my /authorize endpoint.