Apple pay is most likely NOT going to be supported at target, CurrenC seems to be the contactless payment of choice of both Target AND walmart, as well as other places like sears (they are also supported in the beta app).
2 main methods are used for securing the app and payments, #1 every single time you open the app, you need to put in a 4 digit code, and #2 the 3d barcode used changes each time, so even copied it will do no good.
Also lock your phone.
I've been using it and it works quite well. I haven't seen the register side and apparently some prompts come up. It does work fine if they scan it on the item scan screen which is good cause cashiers are always expecting to scan in my discount card first.