Bring your own CA for mTLS

This page explains how you can manage mTLS using client certificates that have not been issued by Cloudflare CA.

This is especially useful if you already have mTLS implemented and client certificates are already installed on devices.

Availability

• Currently, you can only manage your uploaded CA via API, and the hostname associations are not reflected on the dashboard ↗.
• This process is only available on Enterprise accounts.
• Each Enterprise account can upload up to five CAs. This quota does not apply to CAs uploaded through Cloudflare Access.

CA certificate requirements

• The CA certificate can be from a publicly trusted CA or self-signed.
• In the certificate Basic Constraints, the attribute CA must be set to TRUE.
• The certificate must use one of the signature algorithms listed below:

Allowed signature algorithms

x509.SHA1WithRSA

x509.SHA256WithRSA

x509.SHA384WithRSA

x509.SHA512WithRSA

x509.ECDSAWithSHA1

x509.ECDSAWithSHA256

x509.ECDSAWithSHA384

x509.ECDSAWithSHA512

Set up mTLS with your CA

1. Use the Upload mTLS certificate endpoint to upload the CA root certificate.

• ca boolean required

  • Set to true to indicate that the certificate is a CA certificate.

• certificates string required

  • Insert content from the .pem file associated with the CA certificate, formatted as a single string with \n replacing the line breaks.

• name string optional

  • Indicate a unique name for your CA certificate.

2. Take note of the certificate ID (id) that is returned in the API response.
3. Use the Replace Hostname Associations endpoint to enable mTLS in each hostname that should use the CA for mTLS validation. Use the following parameters:

• hostnames array required

  • List the hostnames that will be using the CA for client certificate validation.

    Warning

    Submitting an empty array will remove all hostnames associations.

• mtls_certificate_id string required

  • Indicate the certificate ID obtained from the previous step.

    Warning

    If no mtls_certificate_id is provided, the action will be performed against a Cloudflare Managed CA.

4. (Optional) Since this process is API-only, and hostnames that use your uploaded CA certificate are not listed on the dashboard, you can make a GET request with the mtls_certificate_id as a query parameter to confirm the hostname association.

curl "https://api.cloudflare.com/client/v4/zones/zone_id/certificate_authorities/hostname_associations?mtls_certificate_id={id_from_step_2}"  \
--header "X-Auth-Email: <EMAIL>" \
--header "X-Auth-Key: <API_KEY>"

5. Create a custom rule to enforce client certificate validation. You can do this via the dashboard or via API.

  "expression": "(http.host in {\"<HOSTNAME_1>\" \"<HOSTNAME_2>\"} and not cf.tls_client_auth.cert_verified)",
  "action": "block"

Delete an uploaded CA

If you want to remove a CA that you have previously uploaded, you must first remove any hostname associations that it has.

1. Make a request to the Replace Hostname Associations endpoint, with an empty array for hostnames and specifying your CA certificate ID in mtls_certificate_id:

  "hostnames": [],
  "mtls_certificate_id": "<CERTIFICATE_ID>"

2. Use the Delete mTLS certificate endpoint to delete the certificate.