Can I use Public Key Infrastructure (PKI) as an authentication method in Zendesk?
Zendesk doesn't support authentication through PKI. This sort of authentication relies on sending a new certificate fingerprint every time a user logs in. Zendesk always expects you to send the same certificate, which will be used to extract details such as name or email.
For more information, see the article: SSO (single sign-on) options in Zendesk