What version are you running?
3.0.15
What's the URL of the page this enhancement relates to, if any?
admin/db/scmtools/repository
Describe the enhancement and the motivation for it.
At this moment repository registered in Review Board requires one global user/password. One can limit access into repo making it private, but it requires manual work and synchronisation with some external settings. 

If you have many users or you have repo tree with limited acccess into subdirectories then it is a real pain.

Because of that it would be useful to authenticate user's access into repository by LDAP and limit sources view through it. It would help to avoid manual configuration and would be less error prone.
What operating system are you using? What browser?
ubuntu 18.04, chrome
Please provide any additional information below.