EduGAIN integration

[Robert Jäschke]

Provide support for EduGAIN authentication which would simplify login for academic users.

One important aspect of that is to cleanly integration migration functions, that is, allow users to switch from EduGAIN login to regular password-based login - even in the case their EduGAIN login no longer works. The latter requires to ensure that a valid e-mail address is provided by the provider or by the user.

Some universities provide only very scarce information about their users, thus, users must be allowed to add more information during "registration".

[Robert Jäschke]

Code which facilitates this for Spring Security and which potentially could be re-used (as a library?) can be found at https://github.com/tgradl/dariahsp.