This SocketControlMessage contains a Credentials instance.
It may be sent using send_message and received using receive_message over UNIX
sockets (ie: sockets in the g_socket_family_unix family).
For an easier way to send and receive credentials over stream-oriented UNIX sockets, see
send_credentials and
receive_credentials. To receive credentials of a foreign process
connected to a socket, use get_credentials.
Since GLib 2.72, GUnixCredentialMessage is available on all platforms. It requires underlying system support (such as
Windows 10 with `AF_UNIX`) at run time.
Before GLib 2.72, `<gio/gunixcredentialsmessage.h>` belonged to the UNIX-specific GIO interfaces, thus you had to use the
`gio-unix-2.0.pc` pkg-config file when using it. This is no longer necessary since GLib 2.72.