Update unauthorized message on session expiry

Changed the unauthorized error message to inform users their session has expired and prompt them to log in again. This enhances clarity and user experience by providing a specific reason for the authorization failure.

pic-sure-api-war/src/main/java/edu/harvard/dbmi/avillach/security/JWTFilter.java

@@ -96,7 +96,7 @@ public void filter(ContainerRequestContext requestContext) throws IOException {
                 if (isExplorer) {
                     // If the request is coming from the explorer, we should not allow open access
                     logger.error("User is not authorized.");
-                    requestContext.abortWith(PICSUREResponse.unauthorizedError("User is not authorized."));
+                    requestContext.abortWith(PICSUREResponse.unauthorizedError("Your session has expired. Please log in again."));
                 }
 
                 boolean isAuthorized = callOpenAccessValidationEndpoint(requestContext);