How to use `new tls.TLSSocket(...)` to establish a secure connection?

[armanbilge]

Affected URL(s)

https://nodejs.org/docs/latest-v18.x/api/tls.html

Description of the problem

What is the correct, non-deprecated way to use the new tls.TLSSocket(...) constructor to establish a secure connection? Context: GHSA-2cpx-6pqp-wf35

According to two unmerged docs PRs, when directly calling new tls.TLSSocket(...) it is the user's responsibility to validate peer certificates and identity.

In #10846 it says:

Warning: When directly constructing a tls.TLSSocket instead of using
[tls.connect()][] it is the caller's responsibility to:

• manage the lifetime of the the underlying socket, including connecting it;
• validate the peer certificate and identity, see the ['secure'][] event.

Before using the connection, the user must make the following
checks or the connection should be considered completely insecure:

1. Verify that the peer certificate is valid, see [ssl.verifyError()][].
2. Verify that the peer certificate is for the expected host, see
   [tls.checkServerIdentity()][] and [tls.TLSSocket.getPeerCertificate()][].

In #23915 it says:

It is important to remember, however,
that it is the caller's responsibility to manage the lifecycle of the provided
net.Socket, including establishing the connection and validating peer
certificates and identity. See the ['secure'][] event.

And includes an example:

tlsSocket.on('secure', function() {
  const err = this.verifyError() ||
    tls.checkServerIdentity(hostname, this.getPeerCertificate());
  if (err)
    this.destroy(err);
});

Both PRs demonstrate how to do this validation, but require use of:

1. The 'secure' event. In the current Node.js documentation, the only mention of 'secure' is under the deprecated tls.SecurePair, and is itself deprecated. It is also not clear that the 'secure' event is also emitted on tls.TLSSocket.
   https://nodejs.org/docs/latest-v18.x/api/tls.html#event-secure
2. tlsSocket.ssl.verifyError(), which does not appear at all in the current documentation. Furthermore, according to TLSCallbacks => TLSWrap, better TLS inception #840 (comment) tlsSocket.ssl is a "legacy property".

Note that the described validation steps appear to be consistent with internal use

node/lib/_tls_wrap.js

Line 1106 in 5fbf33e

socket.on('secure', onServerSocketSecure);

node/lib/_tls_wrap.js

Lines 1044 to 1055 in 5fbf33e

	function onServerSocketSecure() {
	if (this._requestCert) {
	const verifyError = this._handle.verifyError();
	if (verifyError) {
	this.authorizationError = verifyError.code;
	if (this._rejectUnauthorized)
	this.destroy();
	} else {
	this.authorized = true;
	}
	}

This leaves me with two concerns:

1. The current documentation does not indicate that using new tls.TLSSocket(...) by itself does not result in a secure connection.
2. As far as I can tell it is impossible to use new tls.TLSSocket(...) to establish a secure connection without relying on APIs that are undocumented, deprecated, and/or legacy.

[mcollina]

@tniessen you might be able to help.