When setting up Raspberry Pi as Digital Signage Player, it's common requirement to set up WiFi configuration ahead of time, so when the Raspberry Pi arrive at location, you only need to connect power and HDMI cable and it's ready to go.
To do so, all you need to do is to edit the wpa_supplicant.conf with WiFi configuration at the location.
Here's the detail steps:
Open Terminal on your Raspberry Pi. Run:
sudo nano /etc/wpa_supplicant/wpa_supplicant.conf
Go to bottom of the file and add the WiFi config in:
Save & Exit (Ctrl+O; Enter then Ctrl+X).
That's it, now if you boot up the Raspberry Pi and the "the-ssid-of-the-wifi-at-location" WiFi is around, the Raspberry Pi will automatically connect to it.
You may want to check the top part of the wpa_supplicant.conf, make sure your Country setting is correct. This helps with troubleshooting and staying in compliance with communication regulations.
country=<Insert country code here> (US, CA, GB, etc.)
If you don't like to store WiFi password in plain text, you can add passphrase to improve 1 level of security.
To do so, add the WiFi by running:
wpa_passphrase "ssid-of-the-wifi" | sudo tee -a /etc/wpa_supplicant/wpa_supplicant.conf > /dev/null