Crear una devolución de llamada del lado del servidor de Inicio de sesión integrado

Nota Este servlet de devolución de llamadas utiliza la codificación en base64 en la respuesta del servidor.

package servlet;

import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.methods.GetMethod;
import org.apache.commons.httpclient.methods.PostMethod;

import org.json.JSONObject;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;
import java.nio.charset.StandardCharsets;
import java.util.Base64;

@WebServlet(
        name = "CallbackServlet2",
        urlPatterns = {"/_callback"}
    )
public class ServerSideCallbacks extends HttpServlet{

	// Client ID
    private static final String CLIENT_ID= 
"3MVG9xOCXq4ID1uF8V6oKd32SPVi6FHwEOQlQ5BjvaKX.5QZpGe4Z3F4fc6KvMYsQ.fi314cp0oZ8KpOBs4Mh";

    // client secret
    private static final String CLIENT_SECRET = "9103416584217247123";
    
    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
        throws 
        ServletException, IOException {

        String code = request.getParameter("code");
        if (code != null) {
            code = URLDecoder.decode(code, "UTF-8");
        }
        String startURL = request.getParameter("state");
        if (startURL != null) {
            startURL = URLDecoder.decode(startURL, "UTF-8");
        }
                
        String tokenResponse = null;
        String communityUrl = null;
        HttpClient httpclient = new HttpClient();
        try {            
            // community_url parameter passed from redirect uri.
            communityUrl = request.getParameter("sfdc_community_url");
            // Token endpoint : communityUrl + "/services/oauth2/token";
            PostMethod post = new PostMethod(communityUrl+"/services/oauth2/token");
            post.addParameter("code",code);
            post.addParameter("grant_type","authorization_code");
            // Consumer key of the external client app.
            post.addParameter("client_id", CLIENT_ID);
            // Consumer Secret of the external client app.
            post.addParameter("client_secret",CLIENT_SECRET);
            
            // Callback URL of the external client app.
            post.addParameter("redirect_uri", 
                "https://boiling-brushlands-41143.herokuapp.com/_callback");
            
            httpclient.executeMethod(post);
            tokenResponse = post.getResponseBodyAsString();
            post.releaseConnection();
 
            System.err.println("tokenResponse: " + tokenResponse);
        } catch (Exception e) {
        		throw new ServletException(e);
        }


        JSONObject identityJSON = null;
        try {
            JSONObject token = new JSONObject(tokenResponse);
            // get the access token from the response
            String accessToken = token.getString("access_token");
            String identity = token.getString("id");
            httpclient = new HttpClient();
            GetMethod get = new GetMethod(identity + "?version=latest");
            get.setFollowRedirects(true);
            get.addRequestHeader("Authorization", "Bearer " + accessToken);
            
            // get identity information using the access token
            httpclient.executeMethod(get);
            String identityResponse = get.getResponseBodyAsString();
            get.releaseConnection();
            identityJSON = new JSONObject(identityResponse);
            identityJSON.put("access_token", accessToken);
        } catch (Exception e) {
            throw new ServletException(e);
        }
        

        response.setContentType("text/html; charset=utf-8");
        PrintWriter out = response.getWriter();

       //  Notice that we’re using base64 encoded
        String outputStr =  "<html><head>\n" +
           "<meta name=\"salesforce-community\" content=\""+ communityUrl +"\">\n" +
            // notice the -callback in the salesforce-mode content value
		         "<meta name=\"salesforce-mode\" content=\"modal-callback\">\n" +
             "<meta name=\"salesforce-server-callback\" content=\"true\">\n" +

		  // send the identity information back to the Embedded Login                
                 "<meta name=\"salesforce-server-response\" content='" + 
                Base64.getEncoder().encodeToString(identityJSON.toString().
                   getBytes(StandardCharsets.UTF_8))+"'>\n" +
                "<meta name=\"salesforce-server-starturl\" content='" + startURL +"'>\n" +
                "<meta name=\"salesforce-target\" content= \"#salesforce-login\">\n"+
                "<meta name=\"salesforce-allowed-domains\" 
                content=\"boiling-brushlands-41143.herokuapp.com\">\n" +
                "<script src=\""+ communityUrl + 
                 "/servlet/servlet.loginwidgetcontroller?type=javascript_widget\"" +
                " async defer></script>\n" +
                "</head><body></body></html>";
        out.write(outputStr);
    }

}