add a way to update the session cookie after every successful request

[cdepillabout]

Ideally, the _GG_SESSION cookie would have its max-age updated after every successful request. This would make sure a user would never have to log back in as long as they were using the upstream application regularly.

Unfortunately, the library we are using to proxy http requests (http-reverse-proxy) doesn't provide any easy way to modify a response.

Right now, the datatype defining how to handle a request is defined like the following:

data WaiProxyResponse = WPRResponse WAI.Response
                        -- ^ Respond with the given WAI Response.
                        --
                        -- Since 0.2.0
                      | WPRProxyDest ProxyDest
                        -- ^ Send to the given destination.
                        --
                        -- Since 0.2.0
                      | WPRProxyDestSecure ProxyDest
                        -- ^ Send to the given destination via HTTPS.
                      | WPRModifiedRequest WAI.Request ProxyDest
                        -- ^ Send to the given destination, but use the given
                        -- modified Request for computing the reverse-proxied
                        -- request. This can be useful for reverse proxying to
                        -- a different path than the one specified. By the
                        -- user.
                        --
                        -- Since 0.2.0
                      | WPRModifiedRequestSecure WAI.Request ProxyDest
                        -- ^ Same as WPRModifiedRequest but send to the
                        -- given destination via HTTPS.
                      | WPRApplication WAI.Application
                        -- ^ Respond with the given WAI Application.

Ideally, this would be changed so that WPRModifiedRequest also took a function for changing the response:

...
| WPRModifiedRequest Request ProxyDest (Response -> Reponse)
...

[cdepillabout]

This issue will require updating the http-reverse-proxy library, so it might take longer than the other issues. This issue should probably be addresses before the other issues in the same milestone.