src,lib: implement experimental DTLS API

Decided to take a short break from the work on QUIC
to implement a DTLS API. Very experimental at this
point but the basic API is there (inspired by the
QUIC API work).

The implementation is based on OpenSSL's built-in
DTLS support and no other dependencies are required.

DTLS is a datagram-based version of TLS that is used
for things like WebRTC and CoAP. It provides similar
security guarantees as TLS but is designed to work over
UDP instead of TCP.

This shouldn't be considered ready for production
but it is a good starting point for experimentation
and feedback.

```bash
./configure --experimental-dtls
make -j{nproc}
./node --experimental-dtls my-dtls-app.js
```

Signed-off-by: James M Snell <jasnell@gmail.com>
Assisted-by: Opencode:Opus 4.6

Author: jasnell

configure.py

@@ -1065,6 +1065,12 @@
     default=None,
     help='build with experimental QUIC support')
 
+parser.add_argument('--experimental-dtls',
+    action='store_true',
+    dest='experimental_dtls',
+    default=None,
+    help='build with experimental DTLS support')
+
 parser.add_argument('--ninja',
     action='store_true',
     dest='use_ninja',
@@ -2350,6 +2356,10 @@ def configure_quic(o):
   o['variables']['node_use_quic'] = b(options.experimental_quic and
                                       not options.without_ssl)
 
+def configure_dtls(o):
+  o['variables']['node_use_dtls'] = b(options.experimental_dtls and
+                                      not options.without_ssl)
+
 def configure_static(o):
   if options.fully_static or options.partly_static:
     if flavor == 'mac':
@@ -2808,6 +2818,7 @@ def make_bin_override():
 configure_v8(output, configurations)
 configure_openssl(output)
 configure_quic(output)
+configure_dtls(output)
 configure_intl(output)
 configure_static(output)
 configure_inspector(output)

doc/api/cli.md

@@ -1212,6 +1212,17 @@ If present, Node.js will look for a
 `node.config.json` file in the current working directory and load it as a
 configuration file.
 
+### `--experimental-dtls`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+Enable experimental support for the DTLS protocol. See the
+[dtls documentation][] for details.
+
 ### `--experimental-eventsource`
 
 <!-- YAML
@@ -3736,6 +3747,7 @@ one is included in the list below.
 * `--experimental-abortcontroller`
 * `--experimental-addon-modules`
 * `--experimental-detect-module`
+* `--experimental-dtls`
 * `--experimental-eventsource`
 * `--experimental-ffi`
 * `--experimental-import-meta-resolve`
@@ -4406,6 +4418,7 @@ node --stack-trace-limit=12 -p -e "Error.stackTraceLimit" # prints 12
 [debugger]: debugger.md
 [debugging security implications]: https://nodejs.org/en/docs/guides/debugging-getting-started/#security-implications
 [deprecation warnings]: deprecations.md#list-of-deprecated-apis
+[dtls documentation]: dtls.md
 [emit_warning]: process.md#processemitwarningwarning-options
 [environment_variables]: #environment-variables_1
 [filtering tests by name]: test.md#filtering-tests-by-name