Redmine

I'm wondering how, when using redmine with active directory, users are authenticated.

I know almost nothing about ldap and active directory, but I understand it's just a database - so does that mean the passwords read by readmine on authentication? In particular, does Active Directory actually store the passwords in the clear rather than as hashes?

Or does readmine just give ldap a username and password for it to authenticate?

Perhaps anyone has some link to a useful read?

Thank you in advance, Jens