Client certificate

The Client Certificate device posture attribute checks if the device has a valid certificate signed by a trusted certificate authority (CA). The posture check can be used in Gateway and Access policies to ensure that the user is connecting from a managed device.

​​ Prerequisites

• A CA that issues client certificates for your devices. WARP does not evaluate the certificate trust chain; this needs to be the issuing certificate.
• Cloudflare WARP client is deployed on the device.
• A client certificate is installed and trusted on the device.

​​ Configure the client certificate check

1. Use the Upload mTLS certificate endpoint Open API docs link to upload the certificate and private key to Cloudflare. The certificate must be a root CA, formatted as a single string with \n replacing the line breaks. The private key is only required if you are using this custom certificate for Gateway HTTPS inspection.

   The response will return a UUID for the certificate:

2. In Zero Trust Open external link , go to Settings > WARP Client.

3. Scroll down to WARP client checks and select Add new.

4. Select Client certificate.

5. You will be prompted for the following information:

   1. Name: Enter a unique name for this device posture check.
   2. Operating system: Select your operating system.
   3. OS locations: Specify the location(s) where the client certificate is installed.

      System	Certificate stores
      Windows	- Local machine trust store - User trust store
      macOS	- System keychain
      Linux	- NSSDB - To search a custom location, enter the absolute file path(s) to the certificate and private key (for example /usr/local/mycompany/certs/client.pem and /usr/local/mycompany/certs/client_key.pem). The certificate and private key must be in PEM format. They can either be in two different files or the same file.

   4. Certificate ID: Enter the UUID of the root CA.
   5. Common name: (Optional) To check for a specific common name on the client certificate, enter a string with optional ${serial_number} and ${hostname} variables (for example, ${serial_number}_mycompany). WARP will search for an exact, case-insensitive match. If you do not specify a common name, WARP will ignore the common name field on the certificate.
   6. Check for Extended Key Usage: (Optional) Check whether the client certificate has one or more attributes set. Supported values are Client authentication (1.3.6.1.5.5.7.3.2) and/or Email (1.3.6.1.5.5.7.3.4).
   7. Check for private key: (Recommended) When enabled, WARP checks that the device has a private key associated with the client certificate.

6. Select Save.

Next, go to Logs > Posture and verify that the client certificate check is returning the expected results.

​​ How WARP checks for a client certificate

Learn how the WARP client determines if a client certificate is installed and trusted on the device.

For the posture check to pass, a certificate must appear in the output that validates against the uploaded root CA.