Please insert your user's login keychain password, so Jenkins is able to unlock it. Normally your login keychain password is the same as your login password, if you haven't changed it explicitly before.

Why does this plugin need access to my login keychain?

Xcode expects to find code signing identities (private key + certificate) in one of your keychains. The login keychain is your default keychain for storing this kind of information and if you've imported a developer identity some time before, it's probably stored in this keychain.

If you want to build a iOS project for your device, you HAVE to use code signing, so you HAVE to insert your credentials here.

Future versions:

It's planned, that this plugin will give you the possibility to manage the whole code singing stuff (importing developer identities, mobile provisioning profiles etc.) from Jenkins' webinterface, so you get rid of some really time consuming and bothersome tasks (think of a distributed environment).