AFAIK,
there are a couple of ways to do it:
1.) USB mode (enter SSID, security type and password)
2.) SoftAP mode (connecting to the AP of the Photon)
3.) Mobile App (probably using the SoftAP feature as well)
The iOS sdk has gone public but probably more to be added before the announcements come official: https://github.com/spark/spark-sdk-ios 