Fix for eclipse-ee4j#25141 - random 403 responses

The securityContext is stateful, cannot be shared among requests. 
RealmAdapter stores the principal from request to it. We need to create 
a copy of the default context for each request instead of 
using the shared default context.

nucleus/security/core/src/main/java/com/sun/enterprise/security/SecurityContext.java

@@ -289,7 +289,8 @@ public static void reset(SecurityContext securityContext) {
     public static SecurityContext getCurrent() {
         SecurityContext securityContext = currentSecurityContext.get();
         if (securityContext == null) {
-            securityContext = defaultSecurityContext;
+            securityContext = generateDefaultSecurityContext();
+            currentSecurityContext.set(securityContext);
         }
 
         return securityContext;