Modifier le fichier /etc/wpa_supplicant/wpa_supplicant.conf:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=FR

network={
	ssid="reseau_beafrancois"
	psk="xxxxxx"
	id_str="montriond"
}

network={
	ssid="Invite"
	psk="xxxxxx"
	id_str="maison"
}

Et créer le fichier /etc/network/interfaces.d/wlan0.conf:

allow-hotplug wlan0
iface wlan0 inet manual
    wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

iface montriond inet dhcp
iface maison inet dhcp