Adding the context around support for 3 integrations (#2505)

Please go to the `Preview` tab and select the appropriate template:

*
[Boundary](?expand=1&labels=Boundary&title=Boundary+Docs&template=boundary_pull_request_template.md)
*
[Consul](?expand=1&labels=Consul&title=Consul+Docs&template=consul_pull_request_template.md)
* [HCP services](?expand=1&template=hcp_pull_request_template.md)
*
[Nomad](?expand=1&labels=Nomad,Runtime&title=Nomad+Docs&template=nomad_pull_request_template.md)

### Terraform

* [HCP
Terraform](?expand=1&labels=hcp,terraform&title=HCP+Terraform+Docs&template=hcp_terraform_pull_request_template.md)
*
[Terraform](?expand=1&labels=terraform&title=Terraform+Docs&template=terraform_pull_request_template.md)
* [Terraform
Enterprise](?expand=1&template=ptfe_release_pull_request_template.md)

Author: schavis

content/vault/v2.x/content/docs/secrets/pki-external-ca/index.mdx

@@ -28,6 +28,10 @@ You can use the PKI external CA plugin to:
 1. **Automate certificate acquisition** through the ACME protocol.
 1. **Cache and distribute certificates** to applications.
 
+The PKI External CA secrets engine is verified to work with
+- [GlobalSign](https://www.hashicorp.com/en/partners/tech/globalsign#all)
+- [Sectigo](https://www.hashicorp.com/en/partners/tech/sectigo#all)
+- [DigiCert](https://www.hashicorp.com/en/partners/tech/digicert#all)
 
 ## Setup