Web Service composition is to construct complex service through combining available services components as request. A service component is a self-contained unit of service construction that provides an identifiable and distinct part of a service with well-defined interface. For example, to assure the security of web service, both the service provider and requestor should take account of the security control. But the implementation of crosscutting concerns, such as security control, will scatter in multiple components.

In this paper we adopt the Aspect-Oriented Programming (AOP) to separate security control from other functional requirements. AOP is a new software development paradigm that aims to increase comprehensibility, adaptability, and reusability by introducing aspect to modularize the crosscutting concerns. Any behavior associated to several components is encapsulated into an aspect. In our work, the composition is extended by weaving extension at running time. It makes the service composition more flexible and gives the composer a chance to unify security policy in composed service by specifying appropriate security extension himself.

This paper also presents an infrastructure to demonstrate how dynamic weaving of aspects can be used to enhance the security of service composition. An application of performing user-defined access control dynamically at run-time is given to exemplify the dynamic extension to service composition.