Move the DomainError marshalling to its own file.
Create a HigherKindedMarshalling trait.
More user tests.
Session creation.
Move readM[T] into a utility trait.
Don't require user's email when using token.

For authentication and for logging out.  This is to simplify the
token-based authentication for the API layer.
Implement the deletion of  a session (logging out).
Stubbed out authentication via user tokens.