In our usage scenario (and, I suspect, many others'), we would like to automatically add LTI users to a group when they are enrolled in a course.  This lets us distinguish them and apply group-based access controls.

I've made a patch to implement this, based on similar code in enrol_meta.

https://github.com/robjoyce/moodle/tree/MDL-62662-enrol_lti_group

Here's the diff page:

https://github.com/moodle/moodle/compare/master...robjoyce:MDL-62662-enrol_lti_group?expand=1 

This is my first contribution to Moodle's code, so let me know if there's something else I need to do as well.  (I don't think I have permission to add a 'patch' label.)

I submitted this back in January as a patch to resolve MDL-62662, but that bug was many years old and I don't think anyone noticed.  Apologies for the duplicate.