I have Apache 2.4 forwarding *:80 traffic to my sole Tomcat 7.0 webapp (Guacamole) like so:
ProxyPass / http://localhost:8080/guacamole/
ProxyPassReverse / http:/localhost:8080/guacamole/
ProxyPassReverseCookiePath / http://localhost:8080/guacamole
HTTP Status 404 - /guacamole/guacamole/index.xhtml
To anyone who stumbles across this issue, I was able to resolve from Suresh Atta's answer to this question.
Basically all that I had to do was create a custom 404 html in /var/lib/tomcat/webapps/guacamole/logout.html which contains a polite message and invitation to log in again:
<html> <h2 align=center>Thank you. You're now logged out.</h2> <h2 align=center>If this was a mistake or you'd like to begin a new session, please <a href="http://guacamoleapp.address.com">click here.</a></h2> </html>
And then I added this directive to web.xml:
<error-page> <error-code>404</error-code> <location>/logout.html</location> </error-page>
I'm sure there's a little cleaner way to do this, but the requirements are low for this right now, and this smoothed the rough edge.