OPA vs OpenFGA: A Comprehensive Technical Comparison of Access Control and Policy Engines
CTO of MadAppGang
Welcome! If you're looking to grasp the distinctions between two distinct methods of authorisation – OPA and OpenFGA – and their respective definitions, you've hit the right spot! In this article, we will answer the most frequently asked questions about them in the simplest and most accessible way possible.
- What are the differences between OPA and OpenFGA?
- When should you use Open Policy Agent, and when is OpenFGA a better choice?
- What are the advantages and disadvantages of each solution?
- How do OPA and OpenFGA implement different authorisation models?
- What are some real-world examples of using OPA or OpenFGA?
- How do the two systems compare in terms of performance?
- In what situations is OPA more suitable than OpenFGA, and vice versa?
We will also provide use cases and share all the necessary technical details.
What is OPA and what is OpenFGA: Their core concepts and purposes
Open Policy Agent (OPA)
It addresses the fundamental challenge of scattered authorization rules across services by providing a unified policy enforcement point that works across cloud-native infrastructure.
- It is a universal policy engine that decouples access decisions from application code.
- Originally developed by Styra in 2016, it is now a CNCF project.
- Authorisation logic is written in the declarative Rego language.
- Its primary purpose is to enable centralised, controlled, and testable access decisions in complex systems.
Source: openpolicyagent.org
allow {
input.user.role == "admin"
input.time < "18:00"
}Ann --(editor)--> Document A
(editor) --> allows "editing"Key architectural differences between OPA and OpenFGA
The architectural differences between OPA and OpenFGA stem from their different authorisation philosophies:
OPA architecture follows the Policy Decision Point model:
OPA evaluates policies against input data and provides structured decision outputs. Policies are written in Rego and can incorporate any JSON-structured data. The engine optimises evaluation through rule indexing and partial evaluation, achieving response times of 26-44 ms for typical RBAC scenarios.
OpenFGA implements a tuple-based relationship model:
OpenFGA uses the relationships between users and resources, stored as simple data entries called tuples, to make authorisation decisions.
It provides APIs such as Check, List Objects, and Expand to determine who has access to what.
The system is designed to respond very quickly — typically in under 10 ms — though more complex configurations may impact its speed.
The following table illustrates the main differences between OPA and OpenFGA:
When to Use OPA or OpenFGA: Use case scenarios
Use OPA when you need to:
- Perform complex policy evaluation with environmental attributes:
- Set time-based access control (e.g., "only during business hours").
- Enforce location-based restrictions (e.g., "only from the corporate network").
- Require specific device or security posture conditions.
- Use multi-factor conditional logic in decisions.
2. Authorise infrastructure and platform access:
- Manage Kubernetes admission control (e.g., via Gatekeeper).
- Control service mesh access (e.g., with Envoy or Istio).
- Secure CI/CD pipelines with policy gates.
- Enforce API gateway access policies.
Example OPA use case: "Allow deployment to production only if: user is in DevOps team AND it's a weekday AND the change has been approved by the security team AND deployment is from the CI/CD system".
Use OpenFGA when you need:
- Relationship-based, hierarchical permissions:
- Provide document sharing with nested folder access.
- Model organisational hierarchies with inherited roles.
- Implement social network-style permissions (e.g., friends, followers).
- Support multi-tenant applications with complex delegation models.
2. Fine-grained, object-level permissions:
- Enable collaborative features similar to Google Drive.
- Set up project management tools with team-based access control.
- Allow detailed sharing in content management systems.
- Manage IoT devices across hierarchical organisations.
Example OpenFGA use case: "A user can edit the document if they are: the owner of the document OR an editor of the parent folder OR an admin of the organisation that owns the folder".
Rego vs OpenFGA DSL: Two ways to define access control
package rbac.authz
# User-role assignments
user_roles := {
"alice": ["engineering", "webdev"],
"bob": ["hr"]
}
# Default deny
default allow := false
# Allow if user has required permission
allow if {
some role in user_roles[input.user]
some permission in role_permissions[role]
permission.action == input.action
permission.resource == input.resource
}
# Complex condition with environmental attributes
allow if {
input.user.clearance_level >= input.resource.classification
is_business_hours
is_corporate_network
}
is_business_hours if {
hour := time.hour(time.now_ns())
hour >= 9
hour <= 17
}model
schema 1.1
type user
type document
relations
define owner: [user]
define editor: [user] or owner
define viewer: [user] or editor
define parent: [folder]
# Inherit permissions from parent folder
define can_view: viewer or viewer from parent
type folder
relations
define owner: [user]
define editor: [user] or owner
define viewer: [user] or editor OPA vs OpenFGA performance: Latency, scalability & optimisation
This infographic compares key performance parameters:
Performance considerations:
- OPA performance depends on policy complexity and data size.
- OpenFGA performance depends on relationship depth and database configuration.
- Both require careful tuning for production workloads.
- Consider caching strategies for both systems.
OPA and OpenFGA integrations: Ecosystem and tooling support
Information about OPA and OpenFGA integrations is below:
Here is a clear comparison of ecosystem maturity:
OPA vs OpenFGA: Pros and cons compared
Let's take a look at the strengths and weaknesses of these two authorisation systems. The OPA advantages are:
- maximum flexibility for any authorization pattern
- mature ecosystem with extensive tooling
- strong infrastructure integration (Kubernetes, service mesh)
- powerful policy language supporting complex logic
- stateless architecture simplifying operations.
But at the same time, OPA has some disadvantages:
- steep learning curve for the Rego language
- no built-in data management requiring custom synchronisation
- complex relationship modeling without native support
- higher initial investment in policy development.
The advantages of OpenFGA are as follows:
- native relationship modeling with inheritance
- built-in reverse queries ("who has access")
- intuitive model for collaborative applications
- proven architecture based on Google Zanzibar
- lower complexity for relationship-based scenarios
OpenFGA has certain disadvantages:
- limited to relationships without environmental attributes
- database dependency adds operational complexity
- less flexibility for non-relational authorisation
- younger ecosystem with fewer resources.
Real-world policy examples: OPA and OpenFGA in action
package api.authorisation
# Environmental access control
default allow := false
allow if {
# Verify authentication
valid_jwt_token
# Check user permissions
user_has_permission
# Verify environmental conditions
request_from_allowed_network
within_business_hours
# Additional MFA for sensitive operations
requires_mfa implies has_valid_mfa
}
# Filter response data based on user role
filtered_response := response if {
input.user.role == "admin"
response := input.data # Admin sees everything
}
filtered_response := response if {
input.user.role == "user"
# Filter to only user's department data
response := [item |
item := input.data[_]
item.department == input.user.department
]
}
user_has_permission if {
required_permission := data.endpoints[input.path].required_permission
required_permission in data.users[input.user.id].permissions
}const authorisationModel = {
type_definitions: [
{
type: "organization",
relations: {
admin: { this: {} },
member: {
union: {
child: [
{ this: {} },
{ computedUserset: { relation: "admin" } }
]
}
}
}
},
{
type: "folder",
relations: {
parent_org: { this: {} },
owner: { this: {} },
editor: {
union: {
child: [
{ this: {} },
{ computedUserset: { relation: "owner" } }
]
}
},
viewer: {
union: {
child: [
{ this: {} },
{ computedUserset: { relation: "editor" } },
{ tupleToUserset: {
tupleset: { relation: "parent_org" },
computedUserset: { relation: "member" }
}}
]
}
}
}
}
]
};
// Check authorization
const { allowed } = await fgaClient.check({
user: 'user:anne',
relation: 'viewer',
object: 'folder:engineering-docs'
});
// List all documents user can view
const { objects } = await fgaClient.listObjects({
user: 'user:anne',
relation: 'viewer',
type: 'document'
}); How to choose between OPA and OpenFGA
Choose OPA for policy-driven authorisation when you need to incorporate complex rules, environmental attributes, or infrastructure-level policies into your authorisation logic, or when you require maximum flexibility. OPA is ideal for scenarios requiring sophisticated policy evaluation, such as those involving complex role or relationship checks.
Opt for OpenFGA for relationship-driven authorisation if your application focuses on collaborative features, hierarchical permissions, or fine-grained, object-level access control. OpenFGA provides an elegant solution for modelling complex permission inheritance and relationship-based access patterns.
We recommend using both in complementary roles. Use OpenFGA to manage application-level relationships and permissions, and OPA to manage infrastructure policies and complex business rules. This hybrid approach combines the strengths of both systems to provide comprehensive authorisation coverage.
While the authorisation landscape continues to evolve, both OPA and OpenFGA are production-ready solutions, backed by strong communities and proven architectures. Your choice should align with your specific authorisation requirements, existing infrastructure, and team expertise.
FAQ section
Q: What is the main difference between OPA and OpenFGA?
A: OPA (Open Policy Agent) is a universal policy engine that enables the definition and enforcement of any type of policy, such as authorisation, validation, and data transformation, using the Rego language. It is often used for ABAC (Attribute-Based Access Control) and RBAC (Role-Based Access Control).
OpenFGA (Open Fine-Grained Authorisation) is a specialised authorisation service based on the Google Zanzibar model. It is designed for relationship-based access control (ReBAC), enabling you to define permissions based on the relationship between objects and users (e.g., 'user owns the document', 'group has access to the folder').
Q: When should I use OPA, and when should I use OpenFGA?
A: Use OPA if:
- You need a universal policy engine for a variety of scenarios (not just authorisation).
- You need to implement complex attribute- or role-based policies.
- You already use Kubernetes, Envoy, or other tools with which OPA integrates well.
- You prefer the declarative language Rego to define policy logic.
Use OpenFGA if:
- Your priority is detailed, granular authorisation based on the relationship between users and resources.
- You are developing a system involving a large number of objects and their relationships, for which traditional RBAC/ABAC would be unwieldy.
- You need a highly scalable and efficient authorisation solution inspired by Google Zanzibar.
- You are looking for an out-of-the-box authorisation service rather than a low-level policy engine.
Q: Can OPA and OpenFGA be used together?
A: Yes, they can be used together, which is often useful. For example:
OpenFGA can define and query relationships (e.g., 'Does User A have an "editor" relationship with Document B?').
OPA can then use this relationship data as input attributes for making more complex policy decisions that also take contextual data into account (e.g., if User A is an editor of Document B but this document is locked, then disallow editing).
Q: Which authorisation model is better: ABAC (Open Policy Authorization) or RBAC (Role-Based Access Control)?
A: Neither model is universally 'better' — the choice depends on your needs.
ABAC (Attribute-Based Access Control), often implemented by OPA, is highly flexible, allowing you to define permissions based on any user, resource, or environmental attributes. It is ideal for complex, context-sensitive policies.
ReBAC (Relationship-Based Access Control), supported by OpenFGA, is effective in scenarios where access is determined by hierarchical or network relationships between entities. It simplifies permission management in systems with a large number of interconnected resources.
Q: How difficult is it to learn and implement OPA and OpenFGA?
A: OPA: Learning the Rego language requires some effort as it is declarative and has its own specific features. However, the OPA community is very active, and there are many resources and examples available. Implementing OPA may require more architectural changes when integrating it into services that require authorisation.
OpenFGA: The Zanzibar concept may be difficult to understand at first, but the modelling language (DSL) is intuitive for defining relationships. Since OpenFGA is a centralized service, its implementation may be simpler from an architectural perspective than a distributed OPA implementation, but it requires a separate service to be deployed and maintained.
Q: Are these tools suitable for a microservice architecture?
A: Absolutely. Both tools are ideal for microservice architecture.
OPA integrates perfectly with API gateways and sidecars (such as Envoy), or can be integrated directly into microservices, enabling decentralised policy enforcement.
OpenFGA, on the other hand, is a centralised service that microservices can call upon to check permissions. This makes managing permissions from a single location easy, which is advantageous in distributed systems.
