Shortest path search in transportation networks is unarguably one of the most important online search services nowadays (e.g., Google Maps, MapQuest, etc), with applications spanning logistics, spatial optimization, or everyday driving decisions. Often times, the owner of the road network data (e.g., a transport authority) provides its database to third-party query services, which are responsible for answering shortest path queries posed by their clients. The issue arising here is that a query service might be returning sub-optimal paths either purposely (in order to serve its own purposes like computational savings or commercial reasons) or because it has been compromised by Internet attackers who falsify the results. Therefore, for the above applications to succeed, it is essential that each reported path is accompanied by a proof, which allows clients to verify the path's correctness. This is the first study on shortest path verification in outsourced network databases. We propose the concept of authenticated hints, which is used to reduce the size of the proofs. We develop several authentication techniques and quantify their tradeoffs with respect to offline construction cost and proof size. Experiments on real road networks demonstrate that our solutions are indeed efficient and lead to compact query proofs.