Security services for workflow systems are becoming increasingly important for the interoperability of cross- enterprises in insecure environments. As a security service, the authorization mechanism for confidentiality and integrity has gained growing attention in both the research world and the industry. However, the traditional workflow authorization model (WAM) mainly focuses on the synchronization of authorization flow by using authorization templates (ATs) and is limited in encountering the consequences of workflow changes and/or exceptions, which are very common in today's dynamic business environment. In this paper, we propose an integrated approach of a flexible WAM with dynamic checking features to handle workflow changes and exceptions. Extended temporal role-based access control and flexible workflow authorization template are adopted to further enhance the traditional AT ensuring information confidentiality and integrity. The method of implementing the proposed model is also introduced.