YARN-8108. Added option to disable loading existing filters to prevent

security filter from initialize twice.
            Contributed by Sunil Govindan

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/webapp/WebApps.java

@@ -83,6 +83,7 @@ static class ServletStruct {
       public String name;
       public String spec;
       public Map<String, String> params;
+      public boolean loadExistingFilters = true;
     }
     
     final String name;
@@ -151,12 +152,13 @@ public Builder<T> withServlet(String name, String pathSpec,
 
     public Builder<T> withServlet(String name, String pathSpec,
         Class<? extends HttpServlet> servlet,
-        Map<String, String> params) {
+        Map<String, String> params,boolean loadExistingFilters) {
       ServletStruct struct = new ServletStruct();
       struct.clazz = servlet;
       struct.name = name;
       struct.spec = pathSpec;
       struct.params = params;
+      struct.loadExistingFilters = loadExistingFilters;
       servlets.add(struct);
       return this;
     }
@@ -256,11 +258,17 @@ public void setup() {
           pathList.add("/" + wsName + "/*");
         }
       }
+
       for (ServletStruct s : servlets) {
         if (!pathList.contains(s.spec)) {
+          // The servlet told us to not load-existing filters, but we still want
+          // to add the default authentication filter always, so add it to the
+          // pathList
+          if (!s.loadExistingFilters) {
             pathList.add(s.spec);
           }
         }
+      }
       if (conf == null) {
         conf = new Configuration();
       }
@@ -333,7 +341,7 @@ public void setup() {
         HttpServer2 server = builder.build();
 
         for(ServletStruct struct: servlets) {
-          if (struct.params != null) {
+          if (!struct.loadExistingFilters) {
             server.addInternalServlet(struct.name, struct.spec,
                 struct.clazz, struct.params);
           } else {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/ResourceManager.java

@@ -1111,7 +1111,7 @@ protected void startWepApp() {
                 "ws")
             .with(conf)
             .withServlet("API-Service", "/app/*",
-                ServletContainer.class, params)
+                ServletContainer.class, params, false)
             .withHttpSpnegoPrincipalKey(
                 YarnConfiguration.RM_WEBAPP_SPNEGO_USER_NAME_KEY)
             .withHttpSpnegoKeytabKey(