You did not look closely enough at Web.config, as there is a membership provider there.
Perhaps also you have not looked closely enough at the documentation or sample projects. There can always be better documentation but many developers have been able to figure out how to get started with what we do have. I do hope to improve the documentation over time, but time is a limited resource and mine is divided many ways. To some extent, the code is the documentation.
See Extending mojoPortal, see the training videos, and study the SampleExternalModule project which is a hello world simple example.
Hope it helps,
Joe