Add a new public function nm_utils_copy_cert_as_user() to libnm. It
reads a certificate or key file on behalf of the given user and writes
it to a directory in /run/NetworkManager. It is useful for VPN plugins
that run as root and need to verify that the user owning the
connection (the one listed in the connection.permissions property) can
access the file.
Add a new command to read the content of a file after switching to the
given user. This command can be used to enforce Unix filesystem
permissions when accessing a file on behalf of a user.