MTLS client certificate propagation

[Verdent]

When MTLS is performed it would be useful for users to have access to the used client certificate over the context.

[astromechza]

I'm going to put up a PR for this as I'm facing just this issue.

[astromechza]

@Verdent / @m0mus Looking at ways to do this I see 2 different approaches:

1. Adding a Getter to the ServerRequest that returns an Optional<X509Certificate>
2. OR, having the ForwardingHandler registering a context key on the request Scope

        // If the client x509 certificate is present on the channel, also add it to the context scope of the ongoing
        // request so that helidon handlers can inspect and react to this.
        Optional.ofNullable(ctx.channel().attr(CLIENT_CERTIFICATE).get())
                .ifPresent(cert -> requestScope.register(WebServerTls.CLIENT_X509_CERTIFICATE, cert));

The latter seems much cleaner, but I'm not sure what the precedent is for registering context items.

Any advice on this?

[trentjeff]

@Verdent - fyi: #4185 - does this satisfy this issue?

[Verdent]

@trentjeff from my point of view it does. @tomas-langer are you OK with not having it in headers?