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.

   curl "https://api.cloudflare.com/client/v4/accounts/{account_id}/mtls_certificates" \
   --header "X-Auth-Email: <EMAIL>" \
   --header "X-Auth-Key: <API_KEY>" \
   --header "Content-Type: application/json" \
   --data '{
     "name": "example_ca_cert",
     "certificates": "-----BEGIN CERTIFICATE-----\nXXXXX\n-----END CERTIFICATE-----",
     "private_key": "-----BEGIN PRIVATE KEY-----\nXXXXX\n-----END PRIVATE KEY-----",
     "ca": true
   }'
   

   The response will return a UUID for the certificate:

   {
   "success": true,
   "errors": [],
   "messages": [],
   "result": {
       "id": "2458ce5a-0c35-4c7f-82c7-8e9487d3ff60",
       "name": "example_ca_cert",
       "issuer": "O=Example Inc.,L=California,ST=San Francisco,C=US",
       "signature": "SHA256WithRSA"
       ...
   }
   

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.

PS C:\Users\JohnDoe> Get-ChildItem Cert:\LocalMachine\My\ | where{$_.Subject -like "*<COMMON_NAME>*"}

PS C:\Users\JohnDoe> Get-ChildItem Cert:\CurrentUser\My\ | where{$_.Subject -like "*<COMMON_NAME>*"}

$ /usr/bin/security find-certificate -c "<COMMON_NAME>" -p /Library/Keychains/System.keychain

$ certutil -L -d sql:/etc/pki/nssdb -r -n <COMMON_NAME>

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