[PROPOSAL] Migrate from Acegi Security to Spring Security

[Jesse Glick]

I have been prototyping a long-discussed replacement of the ancient
Acegi Security library in Jenkins with its maintained Spring Security
successor. At this point, the effort indeed looks feasible. I have
filed a JEP draft which summarizes everything:

https://github.com/jenkinsci/jep/pull/295

Please let me know if you have thoughts on this, either on the mailing
list, the JEP PR, or in one of the code PRs forming the running
“reference implementation”.

[Jesse Glick]

An update here: this has been filed as https://jenkins.io/jep/227 and
is essentially complete. I hope to merge the change into weeklies
after the next LTS line has been cut, in about a month or so. If you
maintain a less common authentication plugin, please take a look at
the compatibility matrix.