crypto: add key type 'dh'

The new key type 'dh' corresponds to EVP_PKEY_DH.

PR-URL: nodejs#31178
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>

doc/api/crypto.md

@@ -1232,6 +1232,9 @@ passing keys as strings or `Buffer`s due to improved security features.
 <!-- YAML
 added: v11.6.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/31178
+    description: Added support for `'dh'`.
   - version: v12.0.0
     pr-url: https://github.com/nodejs/node/pull/26960
     description: Added support for `'rsa-pss'`
@@ -1260,6 +1263,7 @@ types are:
 * `'x448'` (OID 1.3.101.111)
 * `'ed25519'` (OID 1.3.101.112)
 * `'ed448'` (OID 1.3.101.113)
+* `'dh'` (OID 1.2.840.113549.1.3.1)
 
 This property is `undefined` for unrecognized `KeyObject` types and symmetric
 keys.

src/env.h

@@ -194,6 +194,7 @@ constexpr size_t kFsStatsBufferLength =
   V(commonjs_string, "commonjs")                                               \
   V(config_string, "config")                                                   \
   V(constants_string, "constants")                                             \
+  V(crypto_dh_string, "dh")                                                    \
   V(crypto_dsa_string, "dsa")                                                  \
   V(crypto_ec_string, "ec")                                                    \
   V(crypto_ed25519_string, "ed25519")                                          \

src/node_crypto.cc

@@ -3326,6 +3326,8 @@ Local<Value> KeyObject::GetAsymmetricKeyType() const {
     return env()->crypto_rsa_pss_string();
   case EVP_PKEY_DSA:
     return env()->crypto_dsa_string();
+  case EVP_PKEY_DH:
+    return env()->crypto_dh_string();
   case EVP_PKEY_EC:
     return env()->crypto_ec_string();
   case EVP_PKEY_ED25519: