Hello it would be cool to have a authentication via kerberos or remote_user in crowd.
every plugin that would have this feature are either depracted or gone.
there are one issue in crowd that got closed, but its really old:
https://jira.atlassian.com/browse/CWD-461
also there is a confluence issue which didn't get any new responses:
https://jira.atlassian.com/browse/CONF-5875
maybe i missing some other responses.

Also there was a mod_crowd for apache, but still it is depracted:
https://confluence.atlassian.com/display/CROWDEXT/Apache+Basic+Authentication+Module+written+in+c
there isn't any new plugin etc, that gives exactly this functionallity.
but it is the only missing thing, that helds us from buying crowd or that is the only functionallity which says, thats the killer feature of crowd. so that you really need crowd to deploy jira in a kerberos enviroment, either due to kerb auth or remote_user.