Funny thing, you actually can't rely on any answer provided here. I would say the correct approach is to conclude Trac is not that secure (just an assumption) and try to mitigate potential risks.
I assume your goal is to make sure "users" and "developers" can collaborate, but users will not be able to access sources under any circumstances (which is very good, by the way).
There are quite a lot of relevant recipes on the net, but I will provide the simplest one:
- put your Trac behind Apache (you did that already)
- use mod-rewrite to make sure "users" will not get access to [your URL]/browser, ...
- configure Trac permissions as well
- [paranoid mode], change default URLs in order to eliminate guessing
Basically, the idea is to filter users as early as possible in order not to rely on Trac's internal security.
You can also use OWASP Zed Attack Proxy Project to test Trac yourself:

The Zed Attack Proxy (ZAP) is an easy to use integrated penetration
testing tool for finding vulnerabilities in web applications.
It is designed to be used by people with a wide range of security experience
and as such is ideal for developers and functional testers who are new
to penetration testing. ZAP provides automated scanners as well as a
set of tools that allow you to find security vulnerabilities manually.