The current implementation sets the filenames into a static variable, meaning it is shared across all clients and connections.
Errors in the cert or key are only reported if the server reports an authentication failure. Make sure you are passing correct filenames and formats of you do see a failure.
Added February 2, 2022 (dub v10.6)
Sets the client certificate used as a log in identifier on https connections. The certificate and key must be unencrypted at this time and both must be in the same file format.