Export the existing wifi setup

netsh wlan export profile %SSIDName% folder=c:\temp

XML files of the existing connections will be exported to c:temp. Find the one you want all users to access. You need to modify the to false and enter the wireless key.

You will end up with something like this:

<?xml version="1.0"?>
<WLANProfile xmlns="http://www.microsoft.com/networking/WLAN/profile/v1">
<name>Best Network</name>
<SSIDConfig>
<SSID>
<hex>42657374204E6574776F726B</hex>
<name>Best Network</name>
</SSID>
</SSIDConfig>
<connectionType>ESS</connectionType>
<connectionMode>auto</connectionMode>
<MSM>
<security>
<authEncryption>
<authentication>WPA2PSK</authentication>
<encryption>AES</encryption>
<useOneX>false</useOneX>
</authEncryption>
<sharedKey>
<keyType>passPhrase</keyType>
<protected>false</protected>
<keyMaterial>W2kjwoei111</keyMaterial>
</sharedKey>
</security>
</MSM>
</WLANProfile>

Delete the network from Wireless connections, because you need to re-add it for all users, and this will fail if it's already setup.

Reimporting/Adding the WLAN config for all users

netsh wlan add profile filename="wifi.xml" user=all

Note the wifi.xml needs to be modified to match the name of the xml file you wish to import.

The wireless network should now connect before login.