hassox/rails_warden — comment on commit 855eefdc0efe13c656095106cf09f866873516e5
File: lib/rails_warden/controller_mixin.rb line 53
By ttolvane:

I happened to stumble upon the same issue. It seems that since the default unauthenticated_action is always merged to args in RailsWarden's code above, Warden is not able to set the value of :action key from scope_defaults (duplicate key situtation for merge()).

Funny enough, if one sets :action in for RailsWarden's authenticate!() the same applies and the issue can be avoided for now. :)