Organisations are facilitated and conducted using workflow management systems. Currently, we observe a tendency moving away from strict workflow modelling towards dynamic approaches supporting human interactions when deploying a workflow. One specific approach ensuring human-centric workflows is task delegation. Delegating a task may require an access to specific and potentially sensitive data that have to be secured and specified into authorisation policies. In this paper, we propose a modelling approach to secure delegation. In doing so, we define delegation protocols supporting specific constraints based on both workflow and access control systems. Moreover, we develop an advanced access control framework to integrate delegation constraints within existing policies. The novelty consists in the proactivity aspect of our framework to cope with dynamic delegation of authority in authorisation policies.