Open Policy Agent (OPA) is a versatile policy engine designed to handle policy enforcement across cloud infrastructures. It enables users to define and apply policies consistently across a variety of systems, helping maintain security and compliance in dynamic environments.
In my view, OPA represents a significant step forward for cloud infrastructure. From experience, unless a specialized solution is in place, a well-executed OPA implementation can greatly strengthen enterprise software.
Using OPA involves submitting requests as JSON or YAML objects. The engine evaluates these requests against its defined policies and data, producing a determination—essentially a decision of approve or deny. It is then the responsibility of your application to act on this decision.
Decoupling Policy Logic From Business Logic
A key advantage of using OPA is its ability to decouple policy decisions from the business logic in your services. With OPA, the engine determines the outcome of a policy, while your application takes responsibility for enforcing it. This separation makes it possible to manage all policies in a single location, instead of having to update business logic across multiple systems—systems that may be written in different languages and maintained by different teams.
What is Rego?
Regogo is the specialized language used by OPA to define policies. It is a declarative language built for inspecting and manipulating structured data, such as JSON and YAML, which are commonly used to express access rules in cloud environments.
Inspired by Datalogg, Rego extends its capabilities to handle structured document formats like JSON and YAML. While some developers find it challenging to learn, it remains the primary language for OPA users.
How Do You Create an OPA Policy?
Creating an authorization policy in OPA begins with loading your authorization data in a structured format, such as JSON. Next, you write policy rules in Rego to transform this data and establish the authorization context. For example, this might involve identifying a userʼs role or determining which organization owns a particular file. Once the data is properly structured, OPA evaluates it to decide whether a request should be allowed or denied.
How Would You Design RBAC Using OPA?
RBAC, or Role-Based Access Control, is a framework that uses roles to manage user access to resources. The concept of roles is widely understood, and users often expect them as a standard part of any authorization system. For many application developers, defining roles is the quickest and simplest way to start implementing authorization.
To build a role-based access control (RBAC) system using OPA, the first step is assigning roles to your users. This can be represented using a dictionary. For instance, in our example, we have two roles: admin and member. Alice holds both roles, while Bob is only a member.
Next, we define the permissions associated with each role. In this scenario, members can only “readˮ the Acme repository, whereas admins can “writeˮ and “deleteˮ it.
With roles and permissions established, we implement logic to check whether a user can perform a specific action. For any given user, we first determine their assigned roles. Then, we aggregate the permissions across all of their roles to see what actions they are allowed to take.
In this simple example, the policy clearly defines the permissions each user has. With this policy in place, OPA can evaluate whether a user is authorized to perform a requested action.
What Does OPA Do Well?
OPA excels as a general-purpose policy engine. It can ingest data from multiple systems in their native formats, making it highly adaptable. Using its rules language, Rego, you can inspect and transform this data as needed to make authorization decisions. This focus on interoperability makes OPA especially effective when working with third-party systems where you donʼt control the data. Additionally, OPA is well-suited for machine-to-machine operations.
What Are Open Policy Agent Alternatives?
Recently, OPA has hit some community skepticism with OPAʼs main developers being hired by Apple as part of an acquisition of OPAʼs corporate sponsor, Styra.
While OPA will remain open-source, the sunsetting of Styraʼs commercial products has pushed some developers to look for alternatives. One alternative is a platform like Oso. There are, however, some key differences between OPA and Oso (despite the similar name).
Engineering teams are increasingly adopting managed services for core infrastructure, and authorization is no exception. As a result, a growing number of authorization-as-a-service options have emerged alongside self-managed approaches. In this landscape, OPA remains a widely used general-purpose policy engine, implementing authorization as low-level operations on structured data.
