cheald/rack-oauth2-server — comment on commit a582b30e8dd036eb620858e6e5c9d3ddc1ab33f0
File: lib/rack/oauth2/server.rb line 296
By cheald:

When a client makes an authorization request, I want them to be able to pass various information through to the authorize handler. For example, if the client app knows the user's email address, they might want to pass that through so that my application can pre-fill that on the login form. The initial authorization redirect strips any parameters that were passed through during the authorization generation, effectively preventing me from allowing my app to offer auth flow improvements to the client application.