title: Why is traceid sent in automatic 400 responses in ASP.NET Core 2.2
body: <p>ASP.NET Core 2.2 sends <a href="https://docs.microsoft.com/en-us/aspnet/core/web-api/index?view=aspnetcore-2.2#automatic-http-400-responses" rel="nofollow noreferrer">automatic 400 responses</a> for actions which fail model binding and validation.</p>
  
  <p>The result looks like:</p>
  
  <pre><code>{
    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
    "title": "Bad Request",
    "status": 400,
    "traceId": "xyz:xyz"
  }
  </code></pre>
  
  <p>What is <code>traceId</code>, and why is it sent to the client?</p>