Implement logout handler

Fixes entgra/product-iots#113

components/ui-request-interceptor/io.entgra.ui.request.interceptor/src/main/java/io/entgra/ui/request/interceptor/LogoutHandler.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2019, Entgra (Pvt) Ltd. (http://www.entgra.io) All Rights Reserved.
+ *
+ * Entgra (Pvt) Ltd. licenses this file to you 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 io.entgra.ui.request.interceptor;
+
+import io.entgra.ui.request.interceptor.util.HandlerConstants;
+import io.entgra.ui.request.interceptor.util.HandlerUtil;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.http.HttpStatus;
+import org.wso2.carbon.device.application.mgt.common.ProxyResponse;
+
+import javax.servlet.annotation.WebServlet;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import javax.servlet.http.HttpSession;
+import java.io.IOException;
+
+@WebServlet("/logout")
+public class LogoutHandler extends HttpServlet {
+    private static final Log log = LogFactory.getLog(LogoutHandler.class);
+
+    @Override
+    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
+        String serverUrl = req.getScheme() + HandlerConstants.SCHEME_SEPARATOR + req.getServerName()
+                + HandlerConstants.COLON + req.getServerPort();
+        String platform = req.getParameter(HandlerConstants.PLATFORM);
+        HttpSession httpSession = req.getSession(false);
+        if (httpSession != null) {
+            httpSession.invalidate();
+        } else {
+            log.warn("No active session is available. User may not be logged in. Redirecting to the login page");
+        }
+
+        ProxyResponse proxyResponse = new ProxyResponse();
+        proxyResponse.setCode(HttpStatus.SC_OK);
+        proxyResponse.setUrl(serverUrl + HandlerConstants.PATH_SEPARATOR + platform + HandlerConstants.LOGIN_PAGE);
+        try {
+            HandlerUtil.handleSuccess(req, resp, serverUrl, platform, proxyResponse);
+        } catch (IOException e) {
+            log.error("Error occurred when processing logout request.", e);
+        }
+    }
+}

components/ui-request-interceptor/io.entgra.ui.request.interceptor/src/main/java/io/entgra/ui/request/interceptor/util/HandlerConstants.java

@@ -23,9 +23,9 @@ public class HandlerConstants {
     public static final String APP_REG_ENDPOINT = "/api-application-registration/register";
     public static final String UI_CONFIG_ENDPOINT = "/api/application-mgt/v1.0/config/ui-config";
     public static final String TOKEN_ENDPOINT = "/oauth2/token";
+    public static final String LOGIN_PAGE = "/login";
     public static final String BASIC = "Basic ";
     public static final String BEARER = "Bearer ";
-    public static final String COLON = ":";
     public static final String TAGS_KEY = "tags";
     public static final String APP_NAME_KEY = "applicationName";
     public static final String SESSION_AUTH_DATA_KEY = "application-mgt";
@@ -38,6 +38,9 @@ public class HandlerConstants {
     public static final String TOKEN_IS_EXPIRED = "ACCESS_TOKEN_IS_EXPIRED";
 
     public static final String X_PLATFORM_HEADER = "X-Platform";
+    public static final String SCHEME_SEPARATOR = "://";
+    public static final String COLON = ":";
+    public static final String PATH_SEPARATOR = "/";
 
     public static final int INTERNAL_ERROR_CODE = 500;
     public static final long TIMEOUT = 1200;