  In this tutorial, we present an authorization model for distributed systems
that operate with limited internet connectivity. Reliable internet access
remains a luxury for a majority of the world's population. Even for those who
can afford it, a dependence on internet connectivity may lead to sub-optimal
user experiences. With a focus on decentralized deployment, we present an
authorization model that is suitable for scenarios where devices right next to
each other (such as a sensor or a friend's phone) should be able to communicate
securely in a peer-to-peer manner. The model has been deployed as part of an
open-source distributed application framework called Vanadium. As part of this
tutorial, we survey some of the key ideas and techniques used in distributed
authorization, and explain how they are combined in the design of our model.
