1. A method for executing a workflow, implemented on a computer and comprising: providing the workflow comprising process level activities, at least one process level activity being able to access system resources, the access to the system resources being mediated by a plurality of backend modules, the plurality of backend modules comprising intermediate system components and a last backend module, wherein the intermediate system components of the plurality of backend modules each carry out: receiving a hierarchical public-key attribute certificate embedding the rights to access the system resource; validating the attribute certificate; checking whether the attribute certificate grants a right to execute a functional content of the backend module; checking whether a predefined execution path from the process level activity to the backend module has been traversed; if both checking steps are successful, executing the functional content of the backend module; and issuing a new hierarchical public-key certificate for delegating the rights to access a subsequent backend module based on the received hierarchical public-key attribute certificate.