For Web Services in Cloud Computing contexts, the efficient processing of XML documents is a major topic of interest. Especially for WS-Security-enriched messages, processing performance nowadays tends to become a major issue. Streaming XML processing approaches lead to valuable optimization due to lower resource consumption, but their adoption requires major conceptional changes in the processing application.In this paper, we present a pattern for architectural concepts that employ the SAX-based streaming processing approach. Its major benefit--apart from providing the performance advantage--consists in a convenient, modular architecture that can easily be extended with new modules and new types of events without modification of existing modules.