Authorization with Open Policy Agent (OPA)

Authorization is the backbone of building any secure application. It plays a major part in everything from managing access and enforcing application-level permissions effectively to controlling who can access sensitive APIs, validating infrastructure changes, and automating compliance.

Implementing authorization into your application is not an easy thing to do. Traditional approaches of baking authorization logic into your application code often result in scattered rules, tightly coupled logic, and difficulty scaling across systems.

This is where policy engines, and particularly Open Policy Agent (OPA), come into play.

OPA provides a unified, declarative framework for defining and enforcing policies. It can handle access control scenarios like role-based access control (RBAC), attribute-based access control (ABAC), and even relationship-based access control (ReBAC) models, empowering teams to decouple decision-making from application code. Using its policy language, Rego, developers can express rules clearly and consistently across distributed architectures.

In this blog, we will discuss the core principles of using OPA for authorization, how to leverage OPA’s capabilities, write effective policies, and manage them across systems, drawing on real-world expertise shared by Tyler Shade, a seasoned software engineer and core contributor to OPA.

Join Our Livestreams

Before we get started, I’d like to invite you to join our weekly livestreams, which served as the basis for writing this blog. Each session features software development experts who share their insights, tools, and best practices on a wide range of topics, from identity and access management to security and various other software development questions and challenges.

In this particular case, we had the pleasure of hosting Tyler Shade in a session titled “Authorization with Open Policy Agent (OPA)”, where we discussed his extensive experience with OPA, practical tips and advanced use cases.

Tyler shared his approach to solving challenges like data consistency, performance optimization, and plugin development. He also provided valuable advice for managing OPA effectively across large organizations, offering guidance that applies to both beginners and advanced users.

We hope you join us in future sessions - make sure to check out our upcoming livestream calendar.

Without any further adieu, let’s dive into handling Authorization with OPA, starting with the basics - what is OPA, what is Rego, and what are its common use cases.

What is OPA?

Open Policy Agent (OPA) is a general-purpose policy engine that enables you to define and enforce policies using a declarative language called Rego. It provides a powerful framework for making decisions based on your policies and data, whether for managing access control, cloud governance, or infrastructure-as-code validation. As Tyler described it:

“OPA is a framework and toolchain for expressing policies as code and making decisions based on data. You send in your policy and your data, and OPA evaluates the rules to provide a decision.”

OPA allows you to focus on writing high-level policies without worrying about the intricacies of implementation details. This abstraction makes OPA versatile and suitable for various architectures and workflows.

The Rego Policy Language

At the heart of Open Policy Agent (OPA) is Rego, a domain declarative language specifically designed for creating policies.

Policy languages are a formal and structured way of defining rules, conditions, and logic for specifying policies. They provide a standardized syntax and semantics for expressing authorization rules and access control requirements, making it easier to manage and enforce security policies.

Rego enables you to define complex policies declaratively, allowing OPA to evaluate data against these policies and return decisions. Its flexibility and expressiveness make it a powerful tool for defining policies in diverse domains, supporting a wide range of use cases.

OPA and Authorization

While OPA can handle diverse policy needs, one of its most common applications is authorization. Whether implementing role-based access control (RBAC), attribute-based access control (ABAC), or more complex relationship-based access control (ReBAC), it provides a useful framework for defining and enforcing permissions.

How OPA Fits Into Your System

OPA’s flexibility allows it to integrate into a variety of architectures. It can operate as:

• An external decision engine: OPA can run as a standalone service that applications query over HTTP or gRPC to make authorization decisions.
• Embedded within applications: By using OPA’s SDKs, you can integrate its decision-making capabilities directly into your application code.
• Distributed with sidecars: For microservice architectures, OPA sidecars can handle authorization decisions locally, reducing latency and enabling zero-trust security models.

As Tyler Shade mentioned:

“OPA doesn’t just sit in your system—it adapts to your architecture. Whether it’s embedded, centralized, or distributed, it gives you the tools to handle authorization wherever you need it.”

OPA as Part of the Software Development Lifecycle

OPA also integrates well with CI/CD pipelines. OPA should be treated like any other piece of critical software in your system, and, because Rego is code like any other, it should be treated as such.

You’ll write it, test it, debug it, benchmark it, and eventually deploy it using CI/CD pipelines.
There’s no reason not to manage Rego policies alongside your application code using branches, testing, and version control, allowing it to live in the same ecosystem as your application.

For teams leveraging GitOps, OPA’s policy bundles make it straightforward to deliver policy updates efficiently. These bundles can be version-controlled and deployed to OPA instances across the stack, ensuring consistency and scalability.

The issues with Rego don’t stop with treating it as any other code in your CI/CD. Here are some more best practices for handling Rego and its complexity -

Best Practices for Managing Rego

In the case of Rego, with great flexibility comes a learning curve. Tyler noted:

“Rego isn’t the easiest language to learn, especially for developers coming from imperative programming. It requires a shift in thinking, but once you get comfortable, it’s incredibly powerful.”

Managing Rego files effectively is critical as your policy library grows. Treating Rego as code, with all the discipline and tools of modern software development, is only step one to ensure policies are maintainable and scalable. Here are some additional best practices for handling your Rego files:

1. Treat Rego as Code

   Rego is code, and like any other code, it should go through a complete software development lifecycle:

   • Use version control to track changes, enforce branching workflows, and enable reviews.
   • Incorporate testing as part of your development process. Rego includes a robust built-in testing framework, which should be automated in your CI/CD pipelines.

2. Modularity and Structure

   Avoid large, monolithic Rego files. Instead, break your policies into smaller, focused modules based on functionality or service.

   “You wouldn’t write a 10,000-line file in Go, and the same applies to Rego. Break your policies into smaller, manageable files.”

   Modular Rego files not only improve readability but also simplify testing and debugging.

3. Establish Consistent Design Patterns

   With multiple contributors working on policies, consistency is key. Define and enforce coding standards using tools like Rego linters, and perform regular peer reviews to ensure alignment across the team.

4. Use Policy Bundles

   OPA allows you to package Rego files and data into policy bundles. These bundles can be distributed efficiently across environments, ensuring consistency and scalability. GitOps workflows are particularly effective for managing and deploying bundles.

5. Focus on Context-Based Decisions

   Instead of embedding static data into policies, rely on context-based inputs. This reduces the complexity of your Rego files and ensures better performance by offloading dynamic logic to the application layer.

OPA in Action

By incorporating these practices, OPA becomes a reliable cornerstone of your authorization strategy. It brings a unified approach to policy management, integrates smoothly into your development workflows, and ensures that policies remain consistent and scalable across your systems.

As Tyler observed:

“OPA is more than a tool—it’s a platform for managing policies and decisions across your stack. If you treat it like any other critical software, you’ll unlock its full potential.”

By treating Rego as a first-class citizen of your system and embedding OPA into your CI/CD pipelines, you create a scalable, maintainable, and robust authorization solution that grows with your application.

While Rego offers extensive flexibility for writing policies, there are scenarios where extending OPA’s functionality is necessary. This is where OPA’s plugin ecosystem comes in handy.

In the next section, we’ll explore how plugins can extend OPA’s capabilities, enabling even more sophisticated workflows and integrations.

Extending OPA with Plugins

When you explore the Open Policy Agent (OPA) ecosystem, it quickly becomes apparent that its flexibility and extensibility are two of its greatest strengths. For Tyler, this has been a central part of his journey with OPA. Whether helping large enterprises like Geico build scalable systems or enabling organizations to push the boundaries of authorization use cases, plugins have played a critical role in amplifying OPA’s capabilities.

As Tyler described it:

“OPA gives you the flexibility to decide how you want to run it, and plugins add another layer of extensibility when your use case demands it.”

OPA’s plugin ecosystem is where the policy engine transcends its foundational decision-making abilities to become an adaptable tool for diverse applications. Let’s explore this through two real-world examples: Tyler’s work with the Envoy Plugin and how Permit leverages plugins for ReBAC.

Building the Envoy Plugin

When Tyler first started working with OPA, he found customers needed a way to integrate fine-grained authorization into their API gateways. This led him to contribute to the OPA Envoy plugin, which enabled the integration between OPA and the Envoy proxy.

Reflecting on the plugin’s importance, Tyler noted:

“The OPA Envoy plugin makes it possible to use OPA at the edge, extending policy-based decision-making into the realm of service proxies. It’s a great example of how you can embed OPA into existing systems without disrupting workflows.”

Enabling ReBAC at Scale

For Permit.io, plugins have been instrumental in enabling Relationship-Based Access Control (ReBAC)—a model of authorization that evaluates the relationships between entities (like users, groups, and resources). ReBAC is particularly valuable for modern, dynamic applications but can be difficult to implement at scale.

Permit extended OPA’s capabilities by creating a custom Go plugin designed to manage the graph-based data structures required for ReBAC. This plugin supports relationship queries, allowing OPA to handle even the most complex authorization logic efficiently.

As Gabriel highlighted during the livestream:

“We built a custom Go plugin to enable graph-based ReBAC. It’s a challenging use case, but Go’s flexibility and OPA’s plugin architecture made it possible to create something scalable and performant.”

Utilizing OPA’s Full Potential

These two examples have much broader implications when we look at the OPA ecosystem as a whole - OPA’s true power lies not just in its core capabilities but in its ability to grow with your needs through its extensive plugin ecosystem.

This ecosystem serves as the key to unlocking OPA’s full potential, enabling developers to extend this already versatile policy engine into domains and use cases that might have previously been out of reach.

Plugins allow OPA to transcend its role as a decision engine and become a deeply integrated part of an organization’s architecture. They enable developers to craft custom solutions tailored to their unique requirements, enhancing scalability, flexibility, and efficiency. By leveraging plugins, OPA can address challenges far beyond its out-of-the-box functionality, making it a vital component for modern, dynamic applications. As Tyler Shade described it:

“Plugins let you take OPA from being just a standalone decision engine to a critical part of your system. They open the door to use cases you might not even have imagined before.”

Open Policy Administration Layer (OPAL)

One standout example of a plugin capable of significantly extending the functionality of your OPA deployment is the OPAL (Open Policy Administration Layer) open source project.

While OPA excels at evaluating policies and data, it is inherently stateless, which can present challenges in distributed environments or scenarios requiring frequent updates. OPAL addresses this limitation by introducing a control plane and a data plane, enabling real-time policy and data synchronization across OPA instances.

Here’s how OPAL extends OPA’s capabilities:

1. Dynamic Policy Updates

   With OPAL, policy changes can be pushed to OPA instances in real time, without requiring service restarts. This ensures that policies stay up-to-date, even in fast-moving environments.

2. Data Synchronization

   OPAL enables OPA to retrieve and synchronize dynamic data across distributed systems, creating a decentralized architecture. This is particularly valuable for scenarios involving high-frequency updates, such as changes to user permissions or resource attributes.

3. Hybrid Consistency Models

   OPAL offers flexibility in managing data consistency, supporting both strong consistency for critical updates and eventual consistency for less sensitive decisions.

As Tyler pointed out:

“With OPAL, OPA becomes a truly dynamic system. It’s not just evaluating static data—it’s keeping up with changes as they happen, making it perfect for distributed and real-time applications.”

Tyler’s work with Envoy, Permit’s ReBAC implementation, and real-time data synchronizing with OPAL all show the transformative potential of OPA plugins. They enable you to mold OPA into a tool that fits your architecture, no matter how unique or complex your requirements.

OPA’s extensibility ensures that it remains a long-term solution, evolving alongside your applications and unlocking new possibilities as your needs grow.

In Tyler’s words:

“The beauty of OPA plugins is that they let you push boundaries. You can start with OPA as a decision engine and end up with a system tailored perfectly to your use case.”

Key Takeaways and Next Steps

Authorization is one of the most critical aspects of modern software development, and Open Policy Agent (OPA) has proven itself as a transformative tool for managing it effectively. From Rego's capabilities to its seamless integration into diverse architectures and workflows, OPA allows developers to write scalable, consistent, and maintainable policies.

Through this blog, we’ve explored how OPA’s declarative framework simplifies role-based (RBAC), attribute-based (ABAC), and relationship-based (ReBAC) access control. We’ve also seen how integrating OPA into your CI/CD pipelines and treating Rego as code ensures that your authorization logic is as agile and reliable as the systems it governs.

OPA’s real strength, however, lies in its extensibility. The plugin ecosystem, as exemplified by Tyler Shade’s work with the Envoy Plugin, Permit.io’s custom ReBAC solutions, and the OPAL synchronization layer, shows how OPA can adapt to meet even the most demanding, complex needs. These tools transform OPA into more than a policy engine—they make it a cornerstone for managing security, governance, and compliance across modern architectures.

Whether you’re just getting started with authorization or looking to scale your existing systems, OPA provides a path to unify and simplify how you define and enforce policies. By leveraging its core features, adopting best practices, and exploring its plugin ecosystem, you can ensure that your applications remain secure, dynamic, and future-ready.

We encourage you to contribute to the OPA ecosystem and help shape its future. Whether you’re writing Rego policies, creating plugins, or extending tools like OPAL, your contributions make a difference.

Want to learn more about how you can contribute? Join our Slack Community, where there are hundreds of devs building and implementing authorization.