WEBrick servlet for https

I’m writing a servlet subclassed from
WEBrick::HTTPServlet::AbstractServlet
to be used in a WEBrick::HTTPServer over ssl.

When the servlet receives the instance of WEBrick::HTTPRequest passed
into it’s constructor, that instance contains an attribute called
@client_cert.

The server is configured to require and verify a client web browser
certificate,
and everthing works as expected. But @client_cert seems to be always set
to nil.
I need to somehow obtain the .pem encoded client cert, and extract some
of
it’s
elements.

Perhaps I have overlooked something in the instantiation of my servlet,
or the https server itself. Complete documentation of this API seems
scarce.
Any advice or pointers to documentation would be appreciated.