Give the option to not create the service user.

defaults/main.yml

@@ -18,6 +18,7 @@ redmine_download_url: 'http://www.redmine.org/releases'
 #redmine_glob_root_dir: /srv/redmine
 # It is a redmine_glob_root_dir subdirectory
 redmine_inst_dir: redmine
+redmine_create_application_user: True
 redmine_user: redmine
 redmine_group: '{{ redmine_user }}'
 

tasks/redmine.yml

@@ -11,7 +11,13 @@
       - '{{ redmine_glob_users_home_base }}'
 
   - name: Create the user that will run the redmine process
-    user: name={{ redmine_user }} createhome=true home={{ redmine_user_home }} shell=/usr/bin/nologin system=yes
+    user:
+      name: '{{ redmine_user }}'
+      createhome: true
+      home: '{{ redmine_user_home }}'
+      shell: '/usr/bin/nologin'
+      system: yes
+    when: redmine_create_application_user
 
   - name: Ensure that the redmine user can write its $HOME/.subversion to store the svn site ssl certificate
     file: dest={{ redmine_user_home }}/.subversion state=directory owner={{ redmine_user }} group={{ redmine_group }}