No secret option provided to Rack::Session::Cookie warning?
This is a Rails bug, as the subclass is violating the superclass API contract.
The warning can be safely ignored by Rails users.
(https://github.com/rack/rack/issues/485#issuecomment-11956708, emphasis added)
Confirmation on the rails bug discussion: https://github.com/rails/rails/issues/7372#issuecomment-11981397
Reading the discussion based on tehgeekmeisters answer, this warning is popping up as Rails is using Rack cookies in a different way than intended. It should be ok to just ignore this warning for now until there is a final agreement on how to handle this issue and a fix in place.
This issue has been worked around in the just released Rails 3.2.11.
Log: https://github.com/rails/rails/commits/v3.2.11
Commit: https://github.com/rails/rails/commit/95fe9ef945a35f56fa1c3ef356aec4a3b868937c