#Dynamic Verification Policies with OPA and Rego

This guide provides comprehensive documentation for integrating Open Policy Agent (OPA) and Rego policies into a Verifier API. Learn how to define dynamic verification rules for verifiable credentials (VCs) using declarative policies.

#Table of Contents

Introduction
Prerequisites
Installation
Policy Management
Integration with Verifier API
Examples
Troubleshooting
Conclusion

#What is OPA?

Open Policy Agent (OPA) is an open-source policy engine that enables context-aware, dynamic authorization decisions. It uses the Rego language to define policies as code.

#Key Concepts

Rego: Declarative query language for defining policies.
Verifiable Credentials (VCs): Digitally signed credentials that can be programmatically verified.
Dynamic Policies: Rules evaluated at runtime to verify credentials based on custom logic (e.g., checking specific claims).

#Prerequisites

Basic understanding of JSON and REST APIs.
OPA server installed (Installation Guide).
Access to a Verifier API instance.

#Installation

#Step 1: Install OPA

Download and run OPA locally:

# For Linux
wget https://openpolicyagent.org/downloads/v0.46.1/opa_linux_amd64 -O opa
chmod +x opa

# For macOS (Homebrew)
brew install opa

# For Windows (Docker)
docker run -p 8181:8181 openpolicyagent/opa run --server

#Step 2: Start OPA Server

./opa run --server

Default endpoint: http://localhost:8181

#Step 3: Verify Installation

curl http://localhost:8181

#Policy Management

#Policy Structure

Policies are defined in Rego and stored in OPA. A policy consists of:

package: Namespace for the policy (e.g., vc.verification.test).
default allow: Default decision if no rules match.
Rules: Conditions that evaluate to true/false.

#Example Policy

package vc.verification.example

default allow = false

# Allow if credential name matches parameter
allow if {
    input.parameter.name == input.credentialData.credentialSubject.achievement.name
}

#Integration with Verifier API

#Policy Configuration

Include policies in the Verifier API request under request_credentials.policies:

Field	Description
`policy`	Set to `"dynamic"` for OPA-based policies.
`policy_name`	Unique identifier for the policy.
`rules.rego`	Inline Rego policy (or `policy_url` for remote policies).
`argument`	Key-value pairs passed to the policy for evaluation.
`opa_server`	OPA server URL (default: `http://localhost:8181`).
`policy_query`	OPA data query path (e.g., `data.test.allow`).

#Workflow

Verifier API sends the credential data and arguments to OPA.
OPA evaluates the policy against the input.
OPA returns allow: true or allow: false.
Verifier API enforces the decision.

#Examples

#1. Single Condition

Goal: Verify the credential's name matches a specific value.

Request:

{
  "request_credentials": [
    {
      "format": "jwt_vc_json",
      "type": "OpenBadgeCredential",
      "policies": [
        {
          "policy": "dynamic",
          "args": {
            "policy_name": "name_check",
            "rules": {
              "rego": "package vc.verification\n\ndefault allow = false\n\nallow if input.parameter.name == input.credentialData.credentialSubject.name"
            },
            "argument": {
              "name": "JFF x vc-edu PlugFest 3 Interoperability"
            }
          }
        }
      ]
    }
  ]
}

#2. Multiple Conditions (AND Logic)

Goal: Require both name and id to match.

Rego:

package vc.verification

default allow = false

allow if {
    input.parameter.name == input.credentialData.credentialSubject.name
    input.parameter.id == input.credentialData.credentialSubject.id
}

Request:

{
  "args": {
    "argument": {
      "name": "PlugFest 3",
      "id": "urn:uuid:ac254bd5-8fad-4bb1-9d29-efd938536926"
    }
  }
}

#3. Remote Policy URL

Goal: Fetch a policy from a remote server.

Request:

{
  "args": {
    "policy_url": "http://example.com/policies/name_check.rego",
    "opa_server": "http://opa.example.com"
  }
}

Full example:

{
  "request_credentials": [
    {
      "format": "jwt_vc_json",
      "type": "OpenBadgeCredential",
      "policies": [
        {
          "policy": "dynamic",
          "args": {
            "policy_name": "waltid",
            "opa_server": "http://opa.example.com",
            "policy_query": "data",
            "rules": {
              "policy_url": "http://example.com/policies/name_check"
            },
            "argument": {
              "name": "JFF x vc-edu PlugFest 3 Interoperability"
            }
          }
        }
      ]
    }
  ]
}

For advanced use cases, explore OPA’s documentation.

Parameterized Verification Policies Overview