Middleware plugin to apply response headers set before forwarding request

[janko]

This is a follow-up to an older discussion on the Rodauth google group. Currently, when using a Roda app as middleware, any response headers set in the route block are discarded if the request is forwarded to the main app. For Rodauth, this affects extending the remember period, and also possible Authorization header updates when using JWT. In rodauth-rails, I had wrapped the middleware plugin in order to apply the changed response headers, but I consider it a bit of a hack, so I wanted to check if there is interest in an official implementation in the middleware plugin.

I was imagining an additional boolean configuration option for the plugin, where the user can choose whether they want to enable this behaviour. I was thinking the response headers could be stored in Rack env (e.g. roda.headers) before throwing :next in _roda_new_main_route. Then after the main app is called (but before :handle_result is called), the saved headers would be retrieved from env and merged into the headers of the main app's response. I was thinking of excluding Roda's default headers here, which I believe wouldn't be set on response.headers anyway, as neither #finish nor #finish_with_body was called before a request is forwarded.

If this sounds reasonable, I could work on a PR for that.

[jeremyevans]

I agree with adding the feature, and your implementation approach sounds good. Please do submit a PR for it when you have time.