If you’re tired of entering App Store password again and again, even if you download a free application, PasswordPilot is your ultimate companion. PasswordPilot an all new tweak created by Fillipo Biga, automatically enters password for you. You can download it for free on Cydia from the following repo.
Just go to Settings> PasswordPilot and enter your password. The password is stored encrypted, but still carries a risk to your safety. My recommendation is to not install if you have OpenSSH installed, since it is the biggest security hole in jailbreak (unless you have the changed password).