Question

I am using “web server applications” example shown here. In my callback servlet I want to retrieve an access token but I am not able to successfully do it.
Following is my code

  @Override
  protected String getUserId(HttpServletRequest req) throws ServletException, IOException {
    // return user ID
      Iterator<String> iterator = req.getParameterMap().keySet().iterator();
        while (iterator.hasNext()) {
            String string = iterator.next();

            System.out.println(string+"---++--"+req.getParameter(string));
        }
        GoogleAuthorizationCodeTokenRequest newTokenRequest = new GoogleAuthorizationCodeFlow.Builder(new NetHttpTransport(), new JacksonFactory(),
                                                             "2XXXXXX7218.apps.googleusercontent.com", "KugD_XXX_7vqnGZVXXXXX1M",
                                                              Collections.singleton("https://gdata.youtube.com"))
                                                              .build().newTokenRequest(req.getParameter("code"));
        //GoogleAuth
        GoogleTokenResponse token = newTokenRequest.setRedirectUri("/").execute();
        String accessToken = token.getAccessToken();
        System.out.println("accesstoken:"+accessToken);
        return "";
  }

After running this code I am getting following error

com.google.api.client.auth.oauth2.TokenResponseException: 400 Bad Request
{
  "error" : "invalid_request"
}

In a nutshell I am getting the “code” parameter(request code) I am not sure how to convert it to Access token.
I have already seen
Google API – request for token from Oauth2 returns "invalid_request"
Google OAuth 2: response_type error on token request but there wan’t much I could use in my code

EDIT

The google API did not work for me so I wrote following code without using any library

 URL url = new URL("https://accounts.google.com/o/oauth2/token");
    connection = (HttpURLConnection) url.openConnection();
    String urlParameters = "code=" + req.getParameter("code") + "&client_id=29852.apps.googleusercontent.com&client_secret=KugD_LVi_7vqnssssxxxNRBz1M"+
            "&redirect_uri=https://flixomnia.com/oauth2callback&grant_type=authorization_code&scope=https://gdata.youtube.com&response_type=token";
    connection.setDoOutput(true);
    connection.setDoInput(true);
    connection.setInstanceFollowRedirects(true);
    connection.setRequestMethod("POST");
    connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
    connection.setRequestProperty("Authorization", "Bearer 4/q3Xh_pJI458XXXXXXXkh-lxe3-8.cmaD6o7V5BkQXE-XXXXX-edgI");
    connection.setRequestProperty("Content-Length", "" + Integer.toString(urlParameters.getBytes().length));
    connection.setRequestProperty("X-GData-Key", "key=AI39siXXXXXXM7tyHBvXEM1lLcORetit6QSArQ3sjelBxXXXXXXtgLSPdZPxvsF_vkntOQMnAEYAuVFqhN7oUw");
    connection.setRequestProperty("GData-Version", "2");

    connection.setUseCaches(false);
    //com.google.gdata.client.youtube.YouTubeService service = new com.google.gdata.client.youtube.YouTubeService("","");
    //YouTubeMediaGroup g = new YouTubeMediaGroup();


    DataOutputStream wr = new DataOutputStream(connection.getOutputStream());

    wr.writeBytes(urlParameters);
    wr.flush();
    InputStream inputStream = connection.getInputStream();
    byte[] b = new byte[1024];
    while (inputStream.read(b) != -1) {
        System.out.print(new String(b));

    }
    System.out.println("");
    wr.close();
    connection.disconnect();

But still I get following error

    {  "error" : "invalid_request"}
java.io.IOException: Server returned HTTP response code: 400 for URL: https://accounts.google.com/o/oauth2/token
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1615)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
    at com.broadcastr.servlets.YouTubeCallbackService.getUserId(YouTubeCallbackService.java:168)
    at com.google.api.client.extensions.servlet.auth.oauth2.AbstractAuthorizationCodeCallbackServlet.doGet(AbstractAuthorizationCodeCallbackServlet.java:130)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:579)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

Answer 1

1. In the setRedirectUri method in the initial code above to get the access token, the redirect_uri is not set correctly. The redirect_uri that is specified at the time of client registration should be used.

2. In the EDIT code, while sending the required parameters to the access token end-point, an unsupported parameter response_type is also being sent along with the request. Removing the response_type parameter should solve the purpose.

   Also, according to the OAuth2 RFC draft, the access token end-point might also error out invalid_request if the request utilizes more than one mechanism to authenticate the client. So, removing the Authorization header to the URLConnection should also solve the purpose.