Redmine

I found that redmine authentication is based on an internal redmine account, or possibly external LDAP/OpenId accounts.

With plenty of existing apache/svn accounts, a poor sysadmin may wish to reuse this already working apache authentication directly instead of having to setup some LDAP server or to reopen many accounts especially in redmine, and maintain these in parallel.

There may be a way to do this simple task, but it does not stand out of the documentation (HOWTO, search in issues...).
Maybe I'm the only one trying to use redmine on top of existing svn projects?

ISTM that simply putting the hashed Apache login/pass into the users table would not work, as the password hash format does not look the same at all.