There are various methods to find attack patterns for different types of attacks. Apache-scalp is one such tool, but the rule set is not available to find the brute-force attack pattern via regular expression. I would love to know the different regular expressions available for detecting brute-force attacks from Apache log file.
You can just run grep command against Apache access log searching for your login page , use awk to carve out the source ip address then use wc to count how many times a source ip hit your login page. That would be a simple way to check for brute force login attacks from a single source.