Stretch WIFI client

Wireless interfaces are also managed with configuration files in /etc/network/interfaces.d/. For example, to connect as a client to a WPA network with DHCP. Note some or all of this software may already be installed on the target.

Install wpa_supplicant:

apt-get update && apt-get install wpasupplicant -y

Run:

wpa_passphrase youressid yourpassword

This command will output information similar to:

network={
  	ssid="youressid"
  	#psk="yourpassword"
	psk=151790fab3bf3a1751a269618491b54984e192aa19319fc667397d45ec8dee5b
}

Use the hashed PSK in the specific network interfaces file for added security. Create the file /etc/network/interfaces.d/wlan0 with the contents:

allow-hotplug wlan0
iface wlan0 inet dhcp
    wpa-ssid youressid
    wpa-psk 151790fab3bf3a1751a269618491b54984e192aa19319fc667397d45ec8dee5b

To have this take effect immediately:

service networking restart

For more information on configuring Wi-Fi, see Debian's guide here.