Problem
Need to broker requests between clients and the application or service, need to validate and sanitize the requests to provide an additional layer of security.
Cloud services expose endpoints that allow client applications to call their APIs : APIs are exposed to malicious users.
Solution
The gatekeeper pattern can be used to protect storage, or it can be used as a more comprehensive façade to protect all of the functions of the application. This pattern acts like a firewall in a typical network topography. It allows the gatekeeper to examine requests and make a decision about whether to pass the request on to the trusted host that performs the required tasks.
Gatekeeper In Practice