Using google-oauth-java-client to consume a Google App Engine OAuth protected resource

This post shows how to write a java based OAuth client to make requests against a Google App Engine OAuth protected resource using the google-oauth-java-client.

If you want to know how to create an OAuth provider or how to register your domain and get your consumer key and secret, I highly recommend you to read this great blog post written by Ikai Lan.
Actually, you should read it anyway, because the piece of code below just replaces the python script provided by him. Since I needed a java version I decided to write my own client.

The java class below contains a basic junit test which will do the 3-legged OAuth dance. The only thing I haven't implemented is the access token cache part - every time you run this test you will have to explicitly perform the authorization steps in the browser (again).

In  order to run it, you basically have to resolve 2 dependencies:

• google-oauth-java-client
• google-http-java-client

I used the 1.6.0-beta version. Just download and put them in the classpath and you are good to go!

And, of course, don't forget to change the APP_ID and CONSUMER_SECRET constants.

package com.ciandt.oauth.client;

import java.io.BufferedReader;
import java.io.InputStreamReader;

import org.junit.Test;

import com.google.api.client.auth.oauth.OAuthAuthorizeTemporaryTokenUrl;
import com.google.api.client.auth.oauth.OAuthCredentialsResponse;
import com.google.api.client.auth.oauth.OAuthGetAccessToken;
import com.google.api.client.auth.oauth.OAuthGetTemporaryToken;
import com.google.api.client.auth.oauth.OAuthHmacSigner;
import com.google.api.client.auth.oauth.OAuthParameters;
import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestFactory;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;

public class OAuthClientTest {

 private static final HttpTransport TRANSPORT = new NetHttpTransport();
 
 private static final String APP_ID = "your_app_id_here";
 private static final String CONSUMER_KEY = APP_ID + ".appspot.com";
 private static final String CONSUMER_SECRET = "your_consumer_secret_here";
 
 private static final String PROTECTED_SERVICE_URL = "https://" + APP_ID + ".appspot.com/resource";
 private static final String REQUEST_TOKEN_URL = "https://" + APP_ID + ".appspot.com/_ah/OAuthGetRequestToken";
 private static final String AUTHORIZE_URL = "https://" + APP_ID + ".appspot.com/_ah/OAuthAuthorizeToken";
 private static final String ACCESS_TOKEN_URL = "https://" + APP_ID + ".appspot.com/_ah/OAuthGetAccessToken";

 @Test
 public void consumeProtectedResource() throws Throwable {

  // this signer will be used to sign all the requests in the "oauth dance"
  OAuthHmacSigner signer = new OAuthHmacSigner();
  signer.clientSharedSecret = CONSUMER_SECRET;

  // Step 1: Get a request token. This is a temporary token that is used for 
  // having the user authorize an access token and to sign the request to obtain 
  // said access token.
  OAuthGetTemporaryToken requestToken = new OAuthGetTemporaryToken(REQUEST_TOKEN_URL);
  requestToken.consumerKey = CONSUMER_KEY;
  requestToken.transport = TRANSPORT;
  requestToken.signer = signer;

  OAuthCredentialsResponse requestTokenResponse = requestToken.execute();
  
  System.out.println("Request Token:");
  System.out.println("    - oauth_token        = " + requestTokenResponse.token);
  System.out.println("    - oauth_token_secret = " + requestTokenResponse.tokenSecret);

  // updates signer's token shared secret
  signer.tokenSharedSecret = requestTokenResponse.tokenSecret;

  OAuthAuthorizeTemporaryTokenUrl authorizeUrl = new OAuthAuthorizeTemporaryTokenUrl(AUTHORIZE_URL);
  authorizeUrl.temporaryToken = requestTokenResponse.token;
  
  // After the user has granted access to you, the consumer, the provider will
  // redirect you to whatever URL you have told them to redirect to. You can 
  // usually define this in the oauth_callback argument as well.
  String currentLine = "n";
  System.out.println("Go to the following link in your browser:\n"
    + authorizeUrl.build());
  InputStreamReader converter = new InputStreamReader(System.in);
  BufferedReader in = new BufferedReader(converter);
  while (currentLine.equalsIgnoreCase("n")) {
   System.out.println("Have you authorized me? (y/n)");
   currentLine = in.readLine();
  }
  
  // Step 3: Once the consumer has redirected the user back to the oauth_callback
  // URL you can request the access token the user has approved. You use the 
  // request token to sign this request. After this is done you throw away the
  // request token and use the access token returned. You should store this 
  // access token somewhere safe, like a database, for future use.
  OAuthGetAccessToken accessToken = new OAuthGetAccessToken(
    ACCESS_TOKEN_URL);
  accessToken.consumerKey = CONSUMER_KEY;
  accessToken.signer = signer;
  accessToken.transport = TRANSPORT;
  accessToken.temporaryToken = requestTokenResponse.token;

  OAuthCredentialsResponse accessTokenResponse = accessToken.execute();
  System.out.println("Access Token:");
  System.out.println("    - oauth_token        = " + accessTokenResponse.token);
  System.out.println("    - oauth_token_secret = " + accessTokenResponse.tokenSecret);
  System.out.println("\nYou may now access protected resources using the access tokens above.");

  // updates signer's token shared secret
  signer.tokenSharedSecret = accessTokenResponse.tokenSecret;

  OAuthParameters parameters = new OAuthParameters();
  parameters.consumerKey = CONSUMER_KEY;
  parameters.token = accessTokenResponse.token;
  parameters.signer = signer;

  // utilize accessToken to access protected resources
  HttpRequestFactory factory = TRANSPORT.createRequestFactory(parameters);
  GenericUrl url = new GenericUrl(PROTECTED_SERVICE_URL);
  HttpRequest req = factory.buildGetRequest(url);
  HttpResponse resp = req.execute();
  System.out.println("Response Status Code: " + resp.getStatusCode());
  System.out.println("Response body:" + resp.parseAsString());

 }

}