title: OpenAPI parameter with brackets and variable name
body: <p>I am working on an API which allows searching with URLs like:</p>
  
  <pre><code>GET https://example.com/api/data?search[field1]=value1
  GET https://example.com/api/data?search[field2]=value2
  GET https://example.com/api/data?search[field1]=value1&amp;search[field2]=value2
  </code></pre>
  
  <p>Basically, you can search for one or more field values by putting a field name in brackets. The problem is, the field names are defined by the user in their settings. The field name will be a string, but otherwise is not known ahead of time at a global level.</p>
  
  <p><a href="https://stackoverflow.com/a/48498055/446738">This answer</a> is almost what I am looking to do, I just can't find a way to define the value inside the brackets to be "any string" rather than a list of known names.</p>