Zanzibar: Google’s Consistent, Global Authorization System

Determining whether online users are authorized to access
digital objects is central to preserving privacy. This paper presents the design, implementation, and deployment
of Zanzibar, a global system for storing and evaluating access control lists. Zanzibar provides a uniform data model
and configuration language for expressing a wide range of
access control policies from hundreds of client services at
Google, including Calendar, Cloud, Drive, Maps, Photos,
and YouTube. Its authorization decisions respect causal ordering of user actions and thus provide external consistency
amid changes to access control lists and object contents.
Zanzibar scales to trillions of access control lists and millions
of authorization requests per second to support services used
by billions of people. It has maintained 95th-percentile latency of less than 10 milliseconds and availability of greater
than 99.999% over 3 years of production use