title: Get client IP in Koa.js
body: <p>I have a Koa app with a handler like this:</p>
  
  <pre class="lang-js prettyprint-override"><code>router.get('/admin.html', function *(next) {
      const clientIP = "?";
      this.body = `Hello World ${clientIp}`;
  });
  </code></pre>
  
  <p>where I need to acquire the client's IP address to form the response. How can I assign <code>clientIp</code> so it refers to the IP address the request originates from.</p>