title: Adding custom step definitions to Karate framework
body: <p>I have a need to extract a field parsed from a "complex" response header and use that value later in the test.</p>
  
  <p>It seems that the "header" keyword in Karate is set up for setting request headers, not parsing response headers.</p>
  
  <p>Is there a way to add a custom step definition maintaining access to the scenario variable stores?  It appears the variable stores are private in the <code>StepDefs</code> class, and there doesn't seem to be a way to extend it easily. </p>