The Rego language, used primarily with the Open Policy Agent (OPA), is a high-level declarative language for writing policy as code. Here's a basic illustration of how to use Rego:
Example Scenario: User Access Control
Suppose we have a system where we need to control user access based on their roles.
Data Model
First, define a simple data model. In a real-world scenario, this could be JSON data representing user roles and permissions:
{
"users": {
"alice": {"role": "admin"},
"bob": {"role": "developer"},
"eve": {"role": "intern"}
}
}
Policy Definition
Next, write a Rego policy to specify who can access what. For instance, we might want only admins to access sensitive data:
package example
default allow = false
allow {
input.user.role == "admin"
}
In this policy:
- The
package
keyword defines a namespace (example
). -
default allow = false
sets the default decision to deny access. - The
allow
rule permits access if the user's role is "admin".
Query
You'd then query this policy with input data to make access decisions. The input might look like:
{
"user": {"role": "admin"}
}
You'd ask OPA a question like: "Given this input, should access be allowed?" If the input user role is "admin", the policy allows access, returning true
.
Use in Code
In application code, you'd typically integrate OPA as a service or library. The application sends input data (e.g., user information) to OPA and gets back a decision based on your Rego policies.
This example is simplistic but illustrates the basic use of Rego. Real-world scenarios often involve more complex policies, multiple data sources, and integration with services like Kubernetes for dynamic policy enforcement.
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