allow the getTargetSecurityToken can be called as system code

Signed-off-by: Michael Hirsch <michael.hirsch@bosch-si.com>

hawkbit-security-core/src/main/java/org/eclipse/hawkbit/security/SystemSecurityContext.java

@@ -49,6 +49,21 @@ public class SystemSecurityContext {
         this.tenantAware = tenantAware;
     }
 
+    /**
+     * Runs a given {@link Callable} within a system security context, which is
+     * permitted to call secured system code. Often the system needs to call
+     * secured methods by it's own without relying on the current security
+     * context e.g. if the current security context does not contain the
+     * necessary permission it's necessary to execute code as system code to
+     * execute necessary methods and functionality.
+     * 
+     * The security context will be switched to the system code and back after
+     * the callable is called.
+     * 
+     * @param callable
+     *            the callable to call within the system security context
+     * @return the return value of the {@link Callable#call()} method.
+     */
     public <T> T runAsSystem(final Callable<T> callable) {
         final SecurityContext oldContext = SecurityContextHolder.getContext();
         try {
@@ -68,6 +83,17 @@ public class SystemSecurityContext {
         }
     }
 
+    /**
+     * @return {@code true} if the current running code is running as system
+     *         code block.
+     */
+    public boolean isCurrentThreadSystemCode() {
+        if (SecurityContextHolder.getContext().getAuthentication() instanceof SystemCodeAuthentication) {
+            return true;
+        }
+        return false;
+    }
+
     private static void setSystemContext() {
         final SecurityContextImpl securityContextImpl = new SecurityContextImpl();
         securityContextImpl.setAuthentication(new SystemCodeAuthentication());