If you had HTTPS_PROXY=https://some-valid-cert.example.com running a
CONNECT proxy, we should've been able to do a TLS CONNECT request to
e.g. controlplane.tailscale.com:443 through that, and I'm pretty sure
it used to work, but refactorings and lack of integration tests made
it regress.
It probably regressed when we added the baked-in LetsEncrypt root cert
validation fallback code, which was testing against the wrong hostname
(the ultimate one, not the one which we were being asked to validate)
Fixes#16222
Change-Id: If014e395f830e2f87f056f588edacad5c15e91bc
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
e92eb6b17b