Я выяснил свою проблему и нашел довольно простое решение.Мое предположение было верным - поскольку Redmine не знал, как обрабатывать запрос LDAP, он выдал 404.
Ниже приведена правильная конфигурация Apache, позволяющая Redmine (или любой службе, работающей на том же сервере) черезпроцесс аутентификации:
<Location /svn>
# The following two lines allow for any request made by this machine through
# We do this to allow Redmine to have access without needing to authenticate against LDAP
# NOTE: The IP address MUST be the one given by DHCP - the loop-back (127.0.0.1) will NOT WORK
Order allow,deny
Allow from ACTUAL_IP_ADDRESS (example: 123.45.67.100)
# The following authenticates against LDAP for any request NOT made by the same server
# This includes anyone attempting to access:
# http://myserver.com/svn/*
# either via web-browser, or svn command
#
# Tell apache this is a subversion repository
DAV svn
# Where the subversion repository list exists on the file system
SVNParentPath "/var/svn"
# What kind of authentication
AuthType Basic
AuthName "Restricted Subversion Content"
AuthBasicProvider ldap
AuthLDAPBindDN "YOUR_BIND_DN"
AuthLDAPBindPassword "YOUR_BIND_PASSWORD"
AuthLDAPURL "YOUR_LDAP_URL"
# Require a valid-LDAP user (if not from the allowed IP address)
Require valid-user
# This line (very important) tells Apache that the request needs to follow AT LEAST
# one of the following:
# - The request is from the IP address listed above
# - All others MUST authenticate using LDaP
# If we wanted BOTH to be required (not in our case), we would use "Satisfy All"
Satisfy Any
Надеюсь, это поможет кому-то другому, ищущему подобное решение!