Client-side support for TLS Encrypted Client Hello

[0f-0b]

This is a feature request for Encrypted Client Hello (ECH) support in TLS client APIs (Deno.connectTls, Deno.connectQuic, fetch and WebSocket). ECH is a TLS extension that allows clients to encrypt potentially sensitive information in the initial handshake, such as the server name and the ALPN list.

Spec links:

• https://tlswg.org/draft-ietf-tls-esni/draft-ietf-tls-esni.html
• https://tlswg.org/draft-ietf-tls-svcb-ech/draft-ietf-tls-svcb-ech.html

Although the spec is still in draft status, client-side support has already landed in two major browsers – Chrome and Firefox – as well as rustls, the TLS library used by Deno.