header to allow webid tls on servers

as a long time user of solid servers, there is one feature that I cant live
without

and that is the ability to authenticate to a server using WebID / TLS

what this means is that with a simple curl statement and attaching a
certificate you are able to use solid server to server, which is the bulk
of my work flow

recent additions to the authentication suite, involved adding of
webid-oidc, which was promised as an addition, rather than, a replacement

I have tried on a number of occasions to use OIDC with TLS, and it's not
ready, and frankly a large time sink

However, kingsley has been using for some time an innovative approach.  Add
a certain header to your curl request and the server will allow TLS
authentication.  This is in line with the authentication enhancement that
was pitched for solid -- namely oidc to become a point of flexibility.

Mainly a question for Kingsley and the group.  How is this achieved?
Kingsley has stated informally a few times that he sends a webid tls
header.  I need this feature to work.  But two questions

1. What is the name of the header?  Should we try to standardize the naming
in this group?

2. How to patch a server so that it will make use of this functionality.

What the eventual end product would is something like

curl -H "Header : Value" --cert C --key C  URI

And you're done.  Most solid servers do this out of the box already.  But
for those that dont, this would be very useful in allowing server to server
or at least, command line to server requests.