Login details for making app

Hi there,
Just getting started setting the extension up for a customer.

For making an app, in the instructions it says...

1) Log into the Facebook Developer Center at: www.facebook.com/developers
2) Log into Facebook with the account that you want to 'own' your Facebook application
3) Click the "Create New App" button as shown below etc etc

The customer has a profile, and has set up a page too. Do I have to use their profile login details to make the app, or could I be added by them as an admin, login as me, then make the app that way? How would I do this?

It's just they might not want to give me their profile details, but I think I have to be logged in with their profile to make the app. Is this right?

Thanks for your help!

Sorry to double check, but I can't get the customer to use the "Add another admin" link on the 'page' to add me, then I go from there to make the application?

Or is it admins of pages can't make apps?

Thanks again for the quick reply and your patience!