Since RPM 43.19, any file that is installed with explicit ownership
  e.g %attr(, username, groupname)
get's an automatic dependency on user(username) and group(groupname) added, to
ensure the requested ownership can be assigned.

According to
https://en.opensuse.org/openSUSE:Packaging_guidelines#Users_and_Groups
there are two methods to generate the user

* Creating the users using sysuser_tools (prefer)
  As described in above wiki article
  This method adds the user provides/capability automatically to the RPM
metadata

* Creating users/groups in %pre script
  * Any user/group generated like this needs to be advertised in the rpm
metadata using Provides: user(username) and Provides: group(groupname)

Only a single package should ever provide a user