ONOS-1993 Implement API-level permission checking + security util code location replacement

Change-Id: I7bf20eda9c12ed2a44334504333b093057764cd2
diff --git a/core/api/src/main/java/org/onosproject/security/AppGuard.java b/core/api/src/main/java/org/onosproject/security/AppGuard.java
new file mode 100644
index 0000000..d3cc423
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/security/AppGuard.java
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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 org.onosproject.security;
+
+import org.onosproject.core.Permission;
+
+/**
+ * Aids SM-ONOS to perform API-level permission checking.
+ */
+public final class AppGuard {
+
+    private AppGuard() {
+    }
+
+    /**
+     * Checks if the caller has the required permission only when security-mode is enabled.
+     * @param permission permission to be checked
+     */
+    public static void checkPermission(Permission permission) {
+        SecurityManager sm = System.getSecurityManager();
+        if (sm != null) {
+            System.getSecurityManager().checkPermission(new AppPermission(permission.name()));
+        }
+    }
+}