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Concepts

Strong TLS Configuration for Open Policy Agent

Andrios Robert

• 2 min read

The server refused the connection. Your terminal froze for a second. Logs scrolled. The problem wasn’t your policy. It was TLS.

Open Policy Agent (OPA) secures its API endpoints over HTTPS. Without proper TLS configuration, encrypted traffic fails, or worse, accepts unverified connections. Correct setup ensures that OPA talks only to trusted peers and that data in transit stays protected.

Why TLS Matters in OPA

OPA can run as a sidecar, a daemon, or a centralized service. In each mode, remote decisions and data APIs can handle sensitive authorization details. Transport Layer Security prevents interception and enforces identity checks. Misconfigured TLS can expose policy queries or allow man-in-the-middle attacks.

A strong configuration covers:

  • Generating or obtaining valid certificates and keys.
  • Enforcing mutual TLS (mTLS) for client and server authentication.
  • Setting secure cipher suites.
  • Verifying certificate chains and expiration dates.

Basic OPA TLS Configuration

OPA uses flags or configuration files to enable TLS. Example command-line startup:

opa run \
 --server \
 --tls-cert-file=/path/to/server.crt \
 --tls-private-key-file=/path/to/server.key

For mTLS, require client certificates:

opa run \
 --server \
 --tls-cert-file=/path/to/server.crt \
 --tls-private-key-file=/path/to/server.key \
 --tls-ca-cert-file=/path/to/ca.crt

The tls-ca-cert-file option ensures that clients must present certificates signed by a trusted CA. This is essential in sensitive environments where identity verification must be strict.

Best Practices

  • Store TLS private keys in secure, access-controlled locations.
  • Use certificates from a trusted CA or a secure internal PKI.
  • Rotate certificates before expiration.
  • Test your TLS configuration with tools like openssl s_client and automated integration tests.
  • Keep OPA updated to benefit from the latest security fixes and TLS improvements.

OPA TLS with a Config File

Instead of flags, you can configure TLS in an OPA config file:

services:
 example:
 url: https://authz.example.com
 tls:
 cert_file: /etc/opa/certs/client.crt
 private_key_file: /etc/opa/certs/client.key
 ca_cert_file: /etc/opa/certs/ca.crt

server:
 tls_cert_file: /etc/opa/certs/server.crt
 tls_private_key_file: /etc/opa/certs/server.key
 tls_ca_cert_file: /etc/opa/certs/ca.crt

This setup enforces HTTPS everywhere OPA communicates, both inbound and outbound.

Integration Checks

Deploy OPA with TLS in staging before production. Confirm that unauthorized clients are rejected. Monitor logs for TLS handshake errors and certificate warnings. Automate these checks in CI/CD pipelines so broken configs never ship to prod.

Strong TLS configuration for Open Policy Agent is non-negotiable when policies guard critical systems. Set it up once, test it often, keep it current.

See it running with secure TLS now — deploy OPA with hoop.dev and have it live in minutes.