While virtual networks have been subjected to detailed analysis, prototypes are usually constructed and instantiated manually or by means of dedicated control protocols that mostly neglect security considerations. As the instantiation and maintenance of virtual networks requires virtual network operators to gain access to existing network resources, a proper sender authentication builds an important aspect for control protocols. In this work, we present a Virtual Link Setup Protocol (VLSP) that is designed as a modular extension to a standardized state-of-the-art signaling protocol suite. We use these signaling protocols to combine an authenticated and on-demand setup of virtual links with the establishment of Quality-of-Service guarantees in the underlying substrate. The solution presented in this paper is not limited to a specific set of virtualization techniques or tunneling mechanisms. We describe the design and implementation of VLSP and evaluate its signaling performance, as well as the overhead that is associated with the instantiation of the virtual links and the authenticity checks.