We present the design of an outdoor position certification authority. Such an authority aims at certifying the geolocalisation of a mobile device equipped with a global navigation satellite system receiver. Such a receiver is capable of acquiring radio signals (low-level data) and navigation messages (high-level data) in outdoor environments coming from different constellations of global/regional satellite navigation systems and satellite-based augmentation systems. To date, this information is unreliable from a security point of view because it can be easily forged by malicious attackers through specialised spoofing techniques. An outdoor position certification authority defines a client/server architecture through which a user can certify his position by sending the geolocalisation information needed to verify it to one or more remote servers. There are several scenarios for which this service can be very useful and, with the advent of the internet of things age, devices that might require such a service will grow in number.