cert-manager / example-approver-policy-plugin

Example approver policy plugin https://cert-manager.io/docs/projects/approver-policy/#plugins

example-approver-policy-plugin

This repo contains an example cert-manager/approver-policy plugin.

⚠️ This is plugin is not meant to actually be used. This repo does not contain best-practices, production ready code.

Implementing a custom approver plugin

cert-manager/approver-policy can be extended via a plugin mechanism where a custom plugin can be written with specific logic for evaluating CertificateRequests and CertificateRequestPolicys. This can then be registered with the core cert-manager/approver-policy (in Go code) and a single image can be built that will have both the core approver and the custom plugin.

To get started with writing an approver plugin you can clone this repo and change the logic in the methods of the example plugin to do what you want it to do, add tests and the desired packaging mechanism.

The approximate flow when writing an example plugin (that this sample implementation follows):

• implement the cert-manager/approver-policy.Interface. This should contain all the logic of the new plugin for evaluating CertificateRequests and CertificateRequestPolicys.

• ensure that the implementation of approver-policy.Interface is registered with the global approver registry shared with core approver

• build a single Go binary that contains the custom plugin(s) that you wish to use as well as the upstream approver-policy. The entrypoint should be root command of approver-policy

• package the whole project using your favourite packaging mechanism. This repo contains an example Dockerfile and an example Helm chart that includes the core cert-manager/approver-policy's Helm chart.

example plugin

This repo contains an example plugin example-approver-policy-plugin that allows to specify a weekday when CertificateRequests can be approved.

See an example CertificateRequestPolicy that allows issuance only on Tuesdays in ./deploy/examples/tuesday.yaml:

apiVersion: policy.cert-manager.io/v1alpha1
kind: CertificateRequestPolicy
metadata:
  name: tuesday
spec:
  allowed:
    ... # Be aware that using a plugin does not disable the core approver- a CertificateRequest still has to match the allowed block here even if a plugin is specified
  selector:
   ...
  plugins:
    example-approver-policy-plugin:
      values:
        day: "2" # Tuesday (0 - Sunday, 1 - Monday etc)