The question how to handle authorization of digital identities in a service-oriented architecture (SOA) remains an open issue. In this paper we present a design pattern for the integration of legacy systems with SOA using out-of-the-box (unmodified) application servers and discuss how the architecture has to be extended by an Identity Management (IdM) infrastructure. We claim that the IdM infrastructure itself must be designed in a service-oriented way to fit into the overall SOA approach. We introduce a possibility how to decouple the policy enforcement point from the application server and propose an architectural design pattern to seamlessly integrate the SOAs business-related functionality and the IdM infrastructure. An implementation case study illustrates how to apply the invocation pattern for secured web services.