mTLS VerifyClientCertIfGiven, authentication fallback

Feature Request

When using mTLS, it would be nice to use the "VerifyClientCertIfGiven" as the mTLS clientAuthType and if the certificate isn't valid or not given, to fall back to middleware such as basicAuth or ForwardAuth.

I don't believe this is currently possible and I've looked all over the Docs for 2.0.