title: How to update session from within a graphql resolver using apollo-server-epxress
body: <p>I have a graphql server based on apollo-server-express. </p>
  
  <p>My resolvers typically do REST requests on a legacy API. 
  One of the resolvers performs user authentication by sending the username and password to the backend server. The response includes a token that is used for the authentication of subsequent requests.</p>
  
  <p>At the moment I pass the token to my client application includes it in the subsequent requests.</p>
  
  <p>I would now like to save this token in the epxress-session so that it can be then be passed in the context of subsequent resolvers implicitly,</p>
  
  <p>but I don't see how I can update request.session after a response is received in the resolver.</p>