StackTransformer allows plugins to modify Finatra filters before they are applied to controller routes.

Related to the Finagle com.twitter.finagle.StackTransformer, which modifies Finagle server stacks, the Finatra StackTransformer modifies Finatra controller routes.

If the goal is to share functionality between Finagle and Finatra, it's reasonable to want to use Finagle's StackTransformer directly on Finatra routes. However, the unit of functionality, and therefore meaningful reuse, is the stack module - the StackTransformer merely adapts stack modules to various stack contexts.

The stack module as the unit of reuse also makes it possible to install them in specific contexts; for example, modules that should be installed at the service-level but not at the route-level (e.g. admission controllers).