How to get Access Token using client_credentials using java code?

Question

I have some API which requires access token to get the response. In postman we use OAuth 2.0 to get the access token by providing client username and password. In a similar way, I want to fetch the new access token.

Here is the sample code which I have tried so far.

import java.io.*;
import java.net.URL;
import java.net.URLEncoder;
import java.util.Map;
import java.lang.reflect.Type;
import javax.net.ssl.HttpsURLConnection;

// Google Gson Libraries used for Json Parsing
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class AuthGoogle {

    /**
     * @param args
     * @throws IOException 
     */
    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
         String grantType = "client_credentials";
            String applicationID = "application";
            String username = "username";
            String password = "password";
            String url = "url_link";
            HttpsURLConnection httpConn = null;
            BufferedReader in = null;

            try {

                // Create the data to send
                StringBuilder data = new StringBuilder();
                data.append("grant_type=" + URLEncoder.encode(grantType, "UTF-8"));
                data.append("&client_id=" + URLEncoder.encode(applicationID, "UTF-8"));
                data.append("&username=" + URLEncoder.encode(username, "UTF-8"));
                data.append("&password=" + URLEncoder.encode(password, "UTF-8"));

                // Create a byte array of the data to be sent
                byte[] byteArray = data.toString().getBytes("UTF-8");

                // Setup the Request
                URL request = new URL(null, url,  new sun.net.www.protocol.https.Handler());
                httpConn = (HttpsURLConnection)request.openConnection();
                httpConn.setRequestMethod("POST");
                httpConn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
                httpConn.setRequestProperty("Content-Length", "" + byteArray.length);
                httpConn.setDoOutput(true);

                // Write data
                OutputStream postStream = httpConn.getOutputStream();
                postStream.write(byteArray, 0, byteArray.length);
                postStream.close();

                // Send Request & Get Response
                InputStreamReader reader = new InputStreamReader(httpConn.getInputStream());
                in = new BufferedReader(reader);

                // Get the Json reponse containing the Access Token
                String json = in.readLine();
                System.out.println("Json String = " + json);

                // Parse the Json response and retrieve the Access Token
                Gson gson = new Gson();
                Type mapType  = new TypeToken<Map<String,String>>(){}.getType();
                Map<String,String> ser = gson.fromJson(json, mapType);
                String accessToken = ser.get("access_token");
                System.out.println("Access Token = " + accessToken);

            } catch (java.io.IOException e) {

                // This exception will be raised if the server didn't return 200 - OK
                // Retrieve more information about the error
                System.out.println(e.getMessage());

            } finally {

                // Be sure to close out any resources or connections
                if (in != null) in.close();
                if (httpConn != null) httpConn.disconnect();
            }
        }

}

I am getting output as Connection refused: connect.

Another code I have tried is:-

import org.apache.oltu.oauth2.client.OAuthClient;
import org.apache.oltu.oauth2.client.URLConnectionClient;
import org.apache.oltu.oauth2.client.request.OAuthClientRequest;
import org.apache.oltu.oauth2.client.response.OAuthJSONAccessTokenResponse;
import org.apache.oltu.oauth2.common.OAuth;
import org.apache.oltu.oauth2.common.message.types.GrantType;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import org.apache.commons.codec.binary.Base64;

public class OltuJavaClient {

    public static final String TOKEN_REQUEST_URL = "url_link";
    public static final String CLIENT_ID = "client_id";
    public static final String CLIENT_SECRET = "client_pass";

    public static void main(String[] args) {
        try {
            OAuthClient client = new OAuthClient(new URLConnectionClient());

            OAuthClientRequest request =
                    OAuthClientRequest.tokenLocation(TOKEN_REQUEST_URL)
                    .setGrantType(GrantType.CLIENT_CREDENTIALS)
                    .setClientId(CLIENT_ID)
                    .setClientSecret(CLIENT_SECRET)
                    // .setScope() here if you want to set the token scope
                    .buildQueryMessage();
            request.addHeader("Accept", "application/json");
            request.addHeader("Content-Type", "application/json");
            request.addHeader("Authorization", base64EncodedBasicAuthentication());

            String token = client.accessToken(request, OAuth.HttpMethod.POST, OAuthJSONAccessTokenResponse.class).getAccessToken();
            System.out.println(token.toString());

        } catch (Exception exn) {
            exn.printStackTrace();
        }
    }

    private static String base64EncodedBasicAuthentication() {
        // TODO Auto-generated method stub
        return null;
    }
}

Here I am getting this error:- OAuthProblemException{error='unsupported_response_type', description='Invalid response! Response body is not application/json encoded', uri='null', state='null', scope='null', redirectUri='null', responseStatus=0, parameters={}}

Can we do this way? Any leads would be appreciated.

Solution

The best way to get access token using JAVA 11 java.net.http.

Here is the sample code:

//Cliend id and client secret
var keys = "clientid goes here:Client secret goes here";
var URL = "http://localhost:8080/api/token"

HashMap<String, String> parameters = new HashMap<>();
parameters.put("grant_type", "client_credentials");
String form = parameters.keySet().stream()
        .map(key -> key + "=" + URLEncoder.encode(parameters.get(key), StandardCharsets.UTF_8))
        .collect(Collectors.joining("&"));

String encoding = Base64.getEncoder().encodeToString(keys.getBytes());
HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder().uri(URI.create(url))
        .headers("Content-Type", "application/x-www-form-urlencoded", "Authorization", "Basic "+encoding)
        .POST(BodyPublishers.ofString(form)).build();
HttpResponse<?> response = client.send(request, BodyHandlers.ofString());
System.out.println(response.statusCode() + response.body().toString());

Comments

[avidCoder]

I did the changes but still I can see the same error like before.