[Zope] REMOTE_USER Security Issue

My people want to adopt a single sign-on system for web applications that is based on the REMOTE_USER environment variable. I have tried out RemoteUserFolder and also adapted exUserFolder to work similarly. My problem is that I figured out how a user who has permission to create python scripts (might work with dtml and page templates too) could access otherwise forbidden content by making calls that pretend to come from another user. Has any one else come across this problem and devised a solution, either in software or organisation? Problem verified with Zope 2.9.2 and latest RemoteUserFolder. Cliff