Using Additional Context in Policies
Allow rules take in an actor (which comes from authorization logic) and a resource (which comes from mapping). Sometimes you need some additional context information about the environment to write rules over.
For example, let’s say you have a policy like this:
allow(actor, _action, _resource) if actor = "email@example.com";
Here we have a very simple allow rule that allows an actor to access any
resource if they are an admin. Maybe we want to also let any actor access any
resource when the app is in development mode. A typical way to flag that an
app is running in development or production mode would be to set an environment
How would we read that environment variable from our policy though?
We can use a application class that lets us directly access the environment variables:
class Env def self.var(variable) ENV[variable] end end OSO.register_class(Env)
The above class exposes a
var method that reads the application’s environment
variables and returns the requested value. We register the class with Oso,
allowing us to instantiate it in the policy.
We can add a new
allow rule that permits an actor to access a resource if the
application is in development mode:
allow(_actor, _action, _resource) if Env.var("ENV") = "development";
Application classes make it easy to expose any sort of application data to your
policy, including environment variables and request context. This simple
pattern lets you expose any kind of data you want to use in your policy, not
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