Clients use GPG keys to check the authenticity of software packages before they are installed. Only trusted software can be installed on clients.
In most cases, you do not need to adjust the GPG settings to be able to install software on your clients.
RPM packages can be signed directly, while Debian based systems sign only the metadata and use a chain of checksums to secure the packages. Most RPM based systems use signed metadata in addition to signed packages.
Operating systems either trust their own GPG keys directly or at least ship them installed with the minimal system. But third party packages signed by a different GPG key need manual handling. The clients can be successfully bootstrapped without the GPG key being trusted. However, you cannot install new client tool packages or update them until the keys are trusted.
Salt clients use now GPG key information entered for a software channel to manage the trusted keys. When a software channel with GPG key information is assigned to a client, the key gets trusted as soon as the channel is refreshed or the first package gets installed from this channel.
The GPG key URL which is set of a software channel must exist. In case it is a file URL, the GPG key file must be deployed on the client before the software channel is used.
The GPG keys for the Client Tools Channels of Red Hat based clients are deployed on the client into
/etc/pki/rpm-gpg/ and can be referenced with file URLs.