title: How to define header parameters in OpenAPI 3.0?
body: <p>In OpenAPI (Swagger) 2.0, we could define header parameters like so:</p>
  
  <pre class="lang-yaml prettyprint-override"><code>paths:
    /post:
      post:
        parameters:
          - in: header
            name: X-username
  </code></pre>
  
  <p>But in OpenAPI 3.0.0, parameters are replaced by request bodies, and I cannot find a way to define header parameters, which would further be used for authentication.</p>
  
  <p>What is the correct way to define request headers in OpenAPI 3.0.0?</p>