cubicweb #511718 explain why rql expr insertion doesn't work to ease security debugging [open]

Try to explain why such exception occurs

File "src/fcw/cubicweb/server/querier.py", line 270, in _insert_security
  rewrite(myrqlst, lcheckdef, lchecksolutions, self.args)
File "src/fcw/cubicweb/rqlrewrite.py", line 152, in rewrite
  self.insert_snippets(snippets)
File "src/fcw/cubicweb/rqlrewrite.py", line 213, in insert_snippets
  raise Unauthorized()
Unauthorized: You are not allowed to perform this operation

if too expensive at execution time, find a way to check them in a separated tool or at startup.