Add client implementation of hello-mTLS using nodejs

Fixes smallstep/ca-component#138

autocert/examples/hello-mtls/node/client.js

@@ -0,0 +1,44 @@
+const fs = require('fs'); 
+const https = require('https'); 
+
+const config = {
+    ca: '/var/run/autocert.step.sm/root.crt',
+    key: '/var/run/autocert.step.sm/site.key',
+    cert: '/var/run/autocert.step.sm/site.crt',
+    url: process.env.HELLO_MTLS_URL,
+    requestFrequency: 5000
+};
+
+var options = { 
+    ca: fs.readFileSync(config.ca), 
+    key: fs.readFileSync(config.key),
+    cert: fs.readFileSync(config.cert),
+    ciphers: 'ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256',
+    minVersion: 'TLSv1.2',
+    maxVersion: 'TLSv1.2',
+    // Not necessary as it defaults to true
+    rejectUnauthorized: true
+};
+
+fs.watch(config.cert, (event, filename) => {
+    if (event == 'change') {
+        options.cert = fs.readFileSync(config.cert);
+    }
+});
+
+function loop() {
+    var req = https.request(config.url, options, function(res) { 
+        res.on('data', (data) => {
+            process.stdout.write(options.cert)
+            process.stdout.write(data)
+            setTimeout(loop, config.requestFrequency);
+        }); 
+    }); 
+    req.on('error', (e) => {
+        process.stderr.write('error: ' + e.message + '\n');
+        setTimeout(loop, config.requestFrequency);
+    })
+    req.end();
+}
+
+loop();