/usr/lib/ is in ruby-omniauth 1.3.1-1+deb9u1.
This file is owned by root:root, with mode 0o755.
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/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/omniauth/
/usr/lib/ruby/vendor_ruby/omniauth/auth_hash.rb
/usr/lib/ruby/vendor_ruby/omniauth/builder.rb
/usr/lib/ruby/vendor_ruby/omniauth/failure_endpoint.rb
/usr/lib/ruby/vendor_ruby/omniauth/form.css
/usr/lib/ruby/vendor_ruby/omniauth/form.rb
/usr/lib/ruby/vendor_ruby/omniauth/strategies/
/usr/lib/ruby/vendor_ruby/omniauth/strategies/developer.rb
/usr/lib/ruby/vendor_ruby/omniauth/strategy.rb
/usr/lib/ruby/vendor_ruby/omniauth/test/
/usr/lib/ruby/vendor_ruby/omniauth/test/phony_session.rb
/usr/lib/ruby/vendor_ruby/omniauth/test/strategy_macros.rb
/usr/lib/ruby/vendor_ruby/omniauth/test/strategy_test_case.rb
/usr/lib/ruby/vendor_ruby/omniauth/test.rb
/usr/lib/ruby/vendor_ruby/omniauth/version.rb
/usr/lib/ruby/vendor_ruby/omniauth.rb