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+# Client certificate
+
+Client certificate authentication can be configured with the `Client`, the required options are passed along through the `connect` option.
+
+The client certificates must be signed by a trusted CA. The Node.js default is to trust the well-known CAs curated by Mozilla.
+
+Setting the server option `requestCert: true` tells the server to request the client certificate.
+
+The server option `rejectUnauthorized: false` allows us to handle any invalid certificate errors in client code. The `authorized` property on the socket of the incoming request will show if the client certificate was valid. The `authorizationError` property will give the reason if the certificate was not valid.
+
+### Client Certificate Authentication
+
+```js
+const { readFileSync } = require('fs')
+const { join } = require('path')
+const { createServer } = require('https')
+const { Client } = require('undici')
+
+const serverOptions = {
+  ca: [
+    readFileSync(join(__dirname, 'client-ca-crt.pem'), 'utf8')
+  ],
+  key: readFileSync(join(__dirname, 'server-key.pem'), 'utf8'),
+  cert: readFileSync(join(__dirname, 'server-crt.pem'), 'utf8'),
+  requestCert: true,
+  rejectUnauthorized: false
+}
+
+const server = createServer(serverOptions, (req, res) => {
+  // true if client cert is valid
+  if(req.client.authorized === true) {
+    console.log('valid')
+  } else {
+    console.error(req.client.authorizationError)
+  }
+  res.end()
+})
+
+server.listen(0, function () {
+  const tls = {
+    ca: [
+      readFileSync(join(__dirname, 'server-ca-crt.pem'), 'utf8')
+    ],
+    key: readFileSync(join(__dirname, 'client-key.pem'), 'utf8'),
+    cert: readFileSync(join(__dirname, 'client-crt.pem'), 'utf8'),
+    rejectUnauthorized: false,
+    servername: 'agent1'
+  }
+  const client = new Client(`https://localhost:${server.address().port}`, {
+    connect: tls
+  })
+
+  client.request({
+    path: '/',
+    method: 'GET'
+  }, (err, { body }) => {
+    body.on('data', (buf) => {})
+    body.on('end', () => {
+      client.close()
+      server.close()
+    })
+  })
+})
+```