CC Transaction in iPhone apps

Sorry I have some sort of question about iphone apps, this is my first time developing with IOS devices that's why I need some suggestions.

1. Is it allowed to create an apps for IOS devices that contains a transaction with credit card, such as booking reservation or on-line payment/banking?
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2. Lets say that user should log-in first before doing any transaction, for Authentication between the device and web server, any secure way to do this? I mean when logging-in from the device, something like authentication for 1 time login. Any tips or best practice/approach to achieve this?

1. Well, there is that Square app where they give away the reader which plugs into the audio jack, so others have 2) SSL for encrypted xfer?