How to sign app for AppStore in my customer's name

If I'm developing an iPhone app for Compa开发者_StackOverflow社区nyX and when we want to put it on the App Store using CompanyX's signature, and if they dont have the source code, can they do it themselves?

Or do I have to do it with their signature, since I have the source code and then submit it to the App Store?

We have settled on a process where "CompanyX" gives us an account to their iTunes connect so we can build, sign and upload to the App Store in their name.

Probably you can build it on your machine, send them the product and they sign and upload it themselves, however that would be more tedious, as Apple's toolchain with Xcode and the Organizer has become quite good at this for the "usual" case of someone uploading their "own" apps.

AFAIK you have to sign the source code with the key you get from Apple to submit it.