Add an HTTP layer to a tower. This layer
will be called before the 'shiny' app's httpHandler.
Usage
add_http_layer(tower, layer)
Arguments
- tower
A tower
- layer
A function that takes a request and returns either
a response. A layer can short circuit by returning a response
directly or call the next layer will req$NEXT(req) which
will call the next layer in the middleware.
Value
The tower with the added layer