I'm currently working on POC for my company which is looking to use NGINX to validate API Requests using Client Side Certificates. Presently we have it setup so we are self signing/generating these certificates on the local machine and are able to use these successfully in our tests. We are also able to use the revocation list to disable generated certificates.

Moving forward it is possible we will be using an external CA to generate these certificates and we are trying to determine if this is a way to 'whitelist' certificates so only those generated ones which we have visibility of will be verified, rather than a 'blacklisting' approach to block those which are revoked? i.e. Given a client certificate generated by a external CA how can we established this in a trusted list of certs to verify?

Apologies if this question is lacking technical details/knowledge, this is my first hands on experience with SSL.