Add client certificates support

[teabroker]

There should be an ability to add client certificates to the new TLS connection. While this feature is implemented in web clients on the browser side (and not allowed from the code side), it's important to have ability to specify client certificates from code on the server side.

Some apps use client certificates as an authentication technology, so it might be critical.

It could look like an option properties tlsKey, tlsCert or as an object property tls with key and cert properties:

const socket = connect('https://example.com', {
  tls: {
    key: clientKey,
    cert: clientCert,
  },
)

The key and certificate values could be WebCrypto API primitives or TypedArray, ArrayBuffer, DataView instances.

[jasnell]

Definitely agree this is necessary. For a managed environment like workers the key and cert are more likely to be provided by an out-of-band binding configuration, but for unmanaged environments like Node.js, these will need to be provided via configuration options. Will definitely work to get these added.

[teabroker]

It also should be possible to specify or to verify remote end certificate too. It is common API for Node.js and Electron, but not for other runtimes. And it has been requested in Deno (Issue #6170) and Bun (Issue #1044).

It seems like this feature is crucial. And the runtimes seem to have troubles to implement this without having a standard.