Avoid forwarding the client cert from Envoy to ext_proc through a header

[haiyanmeng]

Currently, Envoy forwards the client certificate to ext_proc through the x-forwarded-client-cert header.

• atunnel sends a bare CONNECT request to the egress gateway. The request has Method, URL, and Host and no Header map at all.
• The egress filter chain sets forward_client_cert_details: SANITIZE_SET, so whatever a client sends under this name is discarded and replaced by Envoy's own value.

We should avoid forwarding the client cert from Envoy to ext_proc through a header. The separation of trusted data from Envoy from potential user-supplied data makes it easier to prove the system is secure.

cc Taahir Ahmed (@ahmedtd) Bowei Du (@bowei)

[swiftdiaries]

I'll have some time today after the egress call to work on this.
Not sure if I can do /assign Adhita Selvaraj (@swiftdiaries) ?

[haiyanmeng]

Thanks for picking this up, Adhita Selvaraj (@swiftdiaries) . I assigned it to you.