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Main ACS AEM Commons OSGi Bundle. Includes commons utilities.
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/*
 * ACS AEM Commons
 *
 * Copyright (C) 2013 - 2023 Adobe
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.adobe.acs.commons.aep.impl;

import com.google.gson.JsonObject;
import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.servlets.SlingAllMethodsServlet;
import org.osgi.service.component.annotations.Component;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.Servlet;
import javax.servlet.http.Cookie;
import java.io.IOException;
import java.util.UUID;

import static org.apache.sling.api.servlets.ServletResolverConstants.SLING_SERVLET_PATHS;
import static org.apache.sling.api.servlets.ServletResolverConstants.SLING_SERVLET_METHODS;

@Component(
        service = {Servlet.class},
        property = {
                SLING_SERVLET_PATHS + "=/bin/aep/fpid",
                SLING_SERVLET_METHODS + "=GET"
        }
)
public class FpidCookieServlet extends SlingAllMethodsServlet {
    private static final Logger log = LoggerFactory.getLogger(FpidCookieServlet.class);
    private static final String COOKIE_NAME = "FPID";
    private static final String COOKIE_PATH = "/";
    private static final int COOKIE_MAX_AGE = 60 * 60 * 24 * 30 * 13;
    private static final String JSON_KEY = "fpid";

    @Override
    protected final void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) throws IOException {
        // Try to get an existing FPID cookie
        final Cookie existingCookie = request.getCookie(COOKIE_NAME);

        String cookieValue;

        if (existingCookie == null) {
            //  If no FPID cookie exists, Create a new FPID UUID
            cookieValue = UUID.randomUUID().toString();
        } else {
            // If a FPID cookie exists. get its FPID UUID so it's life can be extended
            cookieValue = existingCookie.getValue();
        }

        // Add the newly generate FPID value, or the extended FPID value to the response
        // Use addHeader(..), as we need to set SameSite=Lax (and addCoookie(..) does not support this)
        response.addHeader("Set-Cookie",
                COOKIE_NAME + "=" + cookieValue + "; " +
                        "Max-Age=" + COOKIE_MAX_AGE + "; " +
                        "Path=" + COOKIE_PATH + "; " +
                        "HttpOnly; " +
                        "Secure; " +
                        "SameSite=Lax");

        // Avoid caching the response in any cache
        response.addHeader("Cache-Control", "no-store");

        // Since the FPID is HttpOnly, JavaScript cannot read it (only the server can)
        // Write the FPID to the response as JSON so client JavaScript can access it.
        final JsonObject json = new JsonObject();
        json.addProperty(JSON_KEY, cookieValue);

        // The JSON `{ fpid: "11111111-2222-3333-4444-55555555" }` is returned in the response
        response.setContentType("application/json");
        response.getWriter().write(json.toString());
    }
}