Certificate Check in an iRule

Hello, I am looking for some guidance on how best to check if a client has a certificate. I would really like to avoid creating a data group with a list of authorization certificates/Hex strings. I have a virtual server with several endpoints. For now I would like to setup a certificate check on just one endpoint. Is there a way in the existing iRule to add some syntax to check to see if a certificate exist when users browse to this one endpoint? if they have a certificate then they are allowed, if no certificate is present then they are rejected,if so what would that syntax look like?

Thanks