We are currently trying to extend the platform (OpenAM 6.5.3) with custom endponints. Is this even possible apart from the standard extension points like (auth nodes/modules, identity stores, etc)? If it is possible, is there some article or documentation describing the process?
I am afraid it may not be possible in version 6.5. That said, if you intend to add custom behaviour to an existing endpoint, you could use Decorator Pattern by proxying that endpoint through IG and add PRE/POST behaviour around a given endpoint.