Our system does not support java.net.http.HttpClient, so I have to use java.net.URLConnection   I got 403 error 403 Forbidden Exception in thread "main" java.io.IOException: Server returned HTTP response code: 403 for URL: https://authz.constantcontact.com/oauth2/default/v1/token?code={authcode}&redirect_uri={url}&grant_type=authorization_code   Here is my Java code,         URL url = new URL("https://authz.constantcontact.com/oauth2/default/v1/token?code="+authCode+"&redirect_uri="+redirectUri+"&grant_type=authorization_code");         HttpURLConnection http = (HttpURLConnection)url.openConnection();         http.setRequestMethod("POST");         http.setDoOutput(true);         http.setRequestProperty("Accept", "application/json");         http.setRequestProperty("Authorization", authHeader);         http.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");         http.setRequestProperty("Content-Length", "0");                 System.out.println(http.getResponseCode() + " " + http.getResponseMessage());                 StringBuffer temp = new StringBuffer();         Scanner scan = new Scanner(http.getInputStream(), "UTF-8");         // Scanner scan = new Scanner(http.getInputStream());         while (scan.hasNext()) {            temp.append(scan.nextLine());         }         scan.close();                     http.disconnect(); ... View more

const client_id = '{client_id}'; const client_secret = '{client_secret}'; const authBase64 = btoa(client_id+':'+client_secret); const redirect_uri = encodeURIComponent('http://localhost/constant-contact/index.html?id=0'); const options = {   method: 'POST',   mode: 'no-cors',   headers: {     'Content-Type': 'application/x-www-form-urlencoded',     Authorization: 'Basic '+authBase64   } }; let code = findGetParameter('code'); if (!code) {   location.href = 'https://authz.constantcontact.com/oauth2/default/v1/authorize?client_id='+client_id+'&response_type=code&scope=contact_data&state=12345&redirect_uri='+redirect_uri; } console.log('code: '+code); document.getElementById('authorization_code').innerText = code; let url = 'https://authz.constantcontact.com/oauth2/default/v1/token?code='+code+'&redirect_uri='+redirect_uri+'&grant_type=authorization_code'; response = fetch(url, options); if (response.ok) {   console.log('response.status: '+response.status);   document.getElementById('response').innerText = response.json(); } ... View more