Session in the context of the OWIN Framework means persisting some data on the server between requests from the same client. Different middleware implementations can choose whether this persistence is for the lifetime of the browser tab or survives browser restarts etc. The OWIN Framework places very few constraints on the implementation, defining the minimum footprint necessary for interoperability only.

For the most part session middleware will have no dependencies and will therefore run at the start of the OWIN pipeline. This means that identification middleware can choose to use session to remember the identity of the caller. In some cases a session middleware developer might want to persist session for a user across multiple browsers or multiple devices and therefore depends on identification. In this case circular dependencies are possible. The OWIN Framework will detect and report these circular dependencies at application startup. In this case the application developer will have to choose an identification middleware that does not depend on session to remember the identity of the client.