RFID anticollision with MFRC522
(too long for a comment)

I'm not sure about "reliably". I'm using a cheap MFRC522 module and the antenna matching seems to be dubious. Thus you commonly get timeouts with multiple cards. The situation seems worse if you change the rx gain from the default (which the linked to code does). If I do that I get all sorts of corruption errors.

In addition, I've never gotten the MFRC522 to do anticollision. With two cards in the field I can get it to detect one card, Halt it and then detect the other immediately but it doesn't run any collision code. I thought the collision register setting would "auto-set to zero" any collision bit but changing that makes no difference. It's a mystery.

Edit: I see other people have gotten anticollision to happen. Thus I think it's an antenna issue or something else. With max antenna gain, I have to move the cards further away to get them to read.