HDDS-2111. XSS fragments can be injected to the S3g landing page

Signed-off-by: Anu Engineer <aengineer@apache.org>

hadoop-ozone/s3gateway/src/main/resources/webapps/static/index.html

@@ -21,6 +21,7 @@
     <meta charset="utf-8">
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="viewport" content="width=device-width, initial-scale=1">
+    <meta http-equiv="Content-Security-Policy" content="script-src 'self';">
     <!-- The above 3 meta tags *must* come first in the head; any other head content must come *after* these tags -->
     <meta name="description" content="Apache Hadoop Ozone S3 gateway">
 
@@ -68,12 +69,15 @@ <h1>S3 gateway</h1>
 
     <p>For example with aws-cli:</p>
 
-    <pre>aws s3api --endpoint <script>document.write(window.location.href.replace("static/", ""))</script> create-bucket --bucket=wordcount</pre>
+    <pre>aws s3api --endpoint <span id="s3gurl"></span> create-bucket --bucket=wordcount</pre>
 
     <p>For more information, please check the <a href="docs">documentation.</a>
     </p>
 </div><!-- /.container -->
 
-<script src="static/bootstrap-3.4.1/js/bootstrap.min.js"></script>
+<script src="jquery-3.4.1.min.js"></script>
+<script src="bootstrap-3.4.1/js/bootstrap.min.js"></script>
+<script src="s3g.js"></script>
+
 </body>
 </html>

hadoop-ozone/s3gateway/src/main/resources/webapps/static/s3g.js

@@ -0,0 +1,23 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.
+ */
+
+window.onload = function () {
+    var safeurl = window.location.protocol + "//" + window.location.host + window.location.pathname;
+    safeurl = safeurl.replace("static/", "");
+    document.getElementById('s3gurl').innerHTML = safeurl;
+};