SLING-3795 : Fields for dynamic references must be volatile

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1613880 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/main/java/org/apache/sling/auth/form/impl/FormAuthenticationHandler.java b/src/main/java/org/apache/sling/auth/form/impl/FormAuthenticationHandler.java
index 361a11d..9314fa3 100644
--- a/src/main/java/org/apache/sling/auth/form/impl/FormAuthenticationHandler.java
+++ b/src/main/java/org/apache/sling/auth/form/impl/FormAuthenticationHandler.java
@@ -289,7 +289,7 @@
      * The resource resolver factory used to resolve the login form as a resource
      */
     @Reference(policy = ReferencePolicy.DYNAMIC, cardinality = ReferenceCardinality.OPTIONAL_UNARY)
-    private ResourceResolverFactory resourceResolverFactory;
+    private volatile ResourceResolverFactory resourceResolverFactory;
 
     /**
      * If true the login form will be presented when the token expires.