My bug report via "M-x debian-bug" include authentication info:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=808378

because I edit package supplied file /etc/tomcat8/tomcat-users.xml.

That come from

  (defun debian-bug-compose-report
    ...
      (debian-bug-prefill-report package severity) ;; <=== HERE

`debian-bug-prefill-report' function call external program:

  $ reportbug --template -T none -s none -S normal -b --list-cc=none --no-bug-script -q tomcat8

In interactive mode reportbug ask you for reviewing any modified files explicitly.

"M-x debian-bug" shown files content also but I see usual text like at top:

control: severity -1 wishlist

let's set the right severity here (it is pretty clear running
reportbug that the information are store publicly "Note: bug reports
are publicly archived (including the email address of the submitter)")
and exists an option (--paranoid) exactly for those more careful about
security and privacy.

I think it is more a task for a bug script in tomcat8, but since
debian-el calls with the --no-bug-scripts... not much can be done from
that side. and even if we do something in reportbug, that will be
ignored since debian-el is running all in automatic-mode, so all the
warnings will be lost.