Column-Level Access Control with Open Policy Agent

Controlling access at the column level is critical for modern data security. Open Policy Agent (OPA) is a lightweight, open source policy engine that makes this possible without burying rules deep inside application code. By defining policies outside your service logic, you keep authorization consistent, auditable, and easy to change.

Why Column-Level Access Matters
Many teams lock data down at the table or row level. That is not enough. Sensitive columns — personal identifiers, financial records, health information — can still leak if policies are too coarse. Column-level access ensures only approved fields are returned for a given user, role, or context.

OPA for Fine-Grained Control
OPA evaluates requests against declarative policies written in Rego. Its decoupled design means you can enforce column-level security in APIs, microservices, or data pipelines without rewriting core logic. You send the request context to OPA. It returns a decision: allow, deny, or transform. This keeps enforcement uniform across all services.

How to Implement Column-Level Access with OPA

1. Model your data fields in the policy input, including the requested columns.
2. Define rules in Rego that decide which columns are visible for each role or condition.
3. Integrate OPA with your service to filter results before sending them to the client.
4. Keep policies in version control for review, testing, and audit.

Example Rego Snippet

package column_access

default allow_columns = []

allow_columns[cols] {
 input.user.role == "admin"
 cols := ["*"]
}

allow_columns[cols] {
 input.user.role == "analyst"
 cols := ["id", "status", "created_at"]
}

In this example, admins see all columns. Analysts see only a defined subset. Any request is checked against these rules before data leaves the service.

Best Practices

• Keep sensitive columns in a separate list in your policy.
• Use versioned policies with automated tests.
• Combine column-level checks with row-level filters for maximum security.
• Enforce in the backend, not the UI, to prevent bypasses.

Open Policy Agent makes column-level access control predictable, centralized, and easy to maintain. You can scope visibility to the exact fields each role needs — nothing more.

See how column-level OPA policies work in practice at hoop.dev and deploy your first secure endpoint in minutes.