Mashups are a new breed of interactive web applications that aggregate and stitch together data retrieved from one or more sources to create an entirely new and innovative set of services. The paradigm is not limited to social networks and many enterprises are redesigning their business processes to create interactive systems in the form of mashups. However, protecting users' private data from unauthorized access in mashups is a challenging security problem. Existing solutions for addressing the various authorization problems are limited due to all-or-nothing policy, third party dependence and scalability issues. In this paper, we present a general permission delegation model for mashups that is fine-grained, user centric and scalable. This contribution has the following objectives: We formally specify the dependency relationships among multiple web applications. Dependency relationships are categorized on the basis of specific data items. We present an extensible reference architecture for configuring multiple web applications and a session management protocol.