The STS implementation in CXF is based on the STS Provider framework in the security runtime, which is essentially an API that can be used to create your own STS implementation. The SEI (Service Endpoint Implementation) contains the following method that can be used for batch processing:
RequestSecurityTokenResponseCollectionType requestCollection(RequestSecurityTokenCollectionType requestCollection)
This method can be used to execute batch processing for any of the core operations (issue/validate/renew/cancel). To do this it is necessary to implement the RequestCollectionOperation interface, and to install it in the STS Provider.