At Charta Software we use HTTP authentication on Linux servers to control access rights for users. Adding access rights for Subversion means adding a new user to Apache (in this case use the code example below) and then specifying the access rights in the /etc/httpd/conf.d/subversion.conf file. The Apache user file for subversion is /var/subversion/users.
Example of adding the Subversion user to Apache:
[user@domain ~]# htpasswd /var/subversion/users username
After changing the Apache configuration file you will have to restart the httpd service