IMPORTANT ANNOUNCEMENT:
Hah, so I guessed this would happen, but Snapchat have decided to check the operating system used for login, compared to the operating system used for other API endpoints.
The login fix I've been using, is that Casper actually logs into Snapchat by pretending to be an iOS device, and then for everything else, pretends to be an Android device.
Snapchat have finally figured this out, and closed that hole, by only allowing the Authentication token received in login, to work for the operating system it was assigned for. (Eg, iPhone, or Android).
So, for the next day or so, (while I work my ass off, getting all the endpoints updated to the iOS flow), unfortunately Casper will not work.
As you say, you're getting logged out as soon as you login...
Sorry for the inconvenience, but we only have Snapchat to thank
I'll try to be fast as possible, but please bare with me, as I can only do soo much in an amount of time
Cheers!