Workflow management systems provide some of the required technical means to preserve integrity, confidentiality and availability at the control-, data- and task assignment layers of a workflow. We currently observe a move away from predefined strict workflow enforcement approaches towards supporting exceptions which are difficult to foresee when modelling a workflow. One specific approach for exception handling is that of task delegation. The delegation of a task from one principal to another, however, has to be managed and executed in a secure way, in this context implying the presence of a fixed set of delegation events. In this paper, we propose first and foremost, a secure task delegation model within a workflow. The novel part of this model is separating the various aspects of delegation with regards tousers, tasks, events and data, portraying them in terms of a multi-layered state machine. We then define delegation scenarios and analyse additional requirements to support secure task delegation over these layers. Moreover, we detail a delegation protocol with a specific focus on the initial negotiation steps between the involved principals.