test: add snicallback prioritization test

Depending on the content of a cert, it seems that OpenSSL
will prioritize the root cert over the context returned by
SNICallback. This behavior is unexpected. This PR adds a
test that demonstrates the behavior. Ideally there is a fix,
or a explanation for this behavior we can add to the docs.

Fixes: nodejs#54235
PR-URL: nodejs#54251

test/parallel/test-https-snicallback-override.js

@@ -0,0 +1,94 @@
+'use strict';
+
+const common = require('../common');
+const { it, describe } = require('node:test');
+const assert = require('node:assert');
+const tls = require('node:tls');
+const https = require('node:https');
+const dns = require('node:dns');
+const events = require('node:events');
+
+const fixtures = require('../common/fixtures');
+const crypto = require('node:crypto');
+
+const root = {
+  cert: fixtures.readKey('ca5-cert.pem'),
+  key: fixtures.readKey('ca5-key.pem')
+};
+
+const agent1 = {
+  cert: fixtures.readKey('agent1-cert.pem'),
+  key: fixtures.readKey('agent1-key.pem')
+};
+
+const PORT = 8443;
+
+const sni = {
+  'ca5.com': {
+    cert: new crypto.X509Certificate(root.cert),
+    secureContext: tls.createSecureContext(root)
+  },
+  'agent1.com': {
+    cert: new crypto.X509Certificate(agent1.cert),
+    context: tls.createSecureContext(agent1),
+  },
+};
+
+const agent = new https.Agent({
+  lookup: (hostname, options, cb) => {
+    if (Object.keys(sni).includes(hostname))
+      hostname = 'localhost';
+    return dns.lookup(hostname, options, cb);
+  }
+});
+
+function makeRequest(url, expectedCert) {
+  return new Promise((resolve, reject) => {
+    https.get(url, { rejectUnauthorized: false, agent }, common.mustCall((response) => {
+      const actualCert = response.socket.getPeerX509Certificate();
+
+      assert.deepStrictEqual(actualCert.subject, expectedCert.subject);
+
+      response.on('data', common.mustCall((chunk) => {
+        assert.strictEqual(chunk.toString(), 'Hello, World!');
+        resolve();
+      }));
+
+      response.on('error', reject);
+    })).on('error', reject);
+  });
+}
+
+describe('Regression test for SNICallback / Certification prioritization issue', () => {
+  it('should use certificates from SNICallback', async (t) => {
+    let snicbCount = 0;
+    const server = https.createServer({
+      cert: root.cert,
+      key: root.key,
+      SNICallback: (servername, cb) => {
+        snicbCount++;
+        // This returns the secure context generated from the respective certificate
+        cb(null, sni[servername].context);
+      }
+    }, (req, res) => {
+      res.writeHead(200);
+      res.end('Hello, World!');
+    }).on('error', common.mustNotCall);
+
+    server.listen(PORT);
+    await events.once(server, 'listening');
+
+    // Assert that raw IP address gets the root cert
+    await makeRequest(`https://127.0.0.1:${PORT}`, sni['ca5.com'].cert);
+
+    for (const [hostname, { cert: expectedCert }] of Object.entries(sni)) {
+      // Currently, the agent1 request will fail as it receives the root cert (ca5) instead.
+      await makeRequest(`https://${hostname}:${PORT}`, expectedCert);
+    }
+
+    // SNICallback should only be called for the hostname requests, not the IP one
+    assert.strictEqual(snicbCount, 2);
+
+    server.close();
+  });
+});