Verify GPG signature: Perform build-time offline GPG verification.
Please verify that included keyring matches your needs.
For manipulation with the offline keyring, please use gpg-offline tool from openSUSE:Factory, devel-tools-building or Base:System.
See the man page and/or /usr/share/doc/packages/gpg-offline/PACKAGING.HOWTO.

If you need to build your package for older products and don't want to mess spec file with ifs, please follow PACKAGING.HOWTO:
you can link or aggregate gpg-offline from
devel:tools:building or use following trick with "osc meta prjconf":

--- Cut here ----
%if 0%{?suse_version} <= 1220
Substitute: gpg-offline
%endif

Macros:
%gpg_verify(dnf) \
%if 0%{?suse_version} > 1220\
echo "WARNING: Using %%gpg_verify macro from prjconf, not from gpg-offline package."\
gpg-offline --directory="%{-d:%{-d*}}%{!-d:%{_sourcedir}}" --package="%{-n:%{-n*}}%{!-n:%{name}}""%{-f: %{-f*}}" --verify %{**}\
%else\
echo "WARNING: Dummy prjconf macro. gpg-offline is not available, skipping %{**} GPG signature verification!"\
%endif\
%nil
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