[Pay] entering ubuntu one password for purchases can be a pain

I understand that we want to make it difficult for not authorised people to be able to buy apps on the phone, but whilst I understand we want the purchases be tied to an Ubuntu One account, entering that password each time I want to buy something seems a bit excessive for me.
I have a (purposefully) complex password for Ubuntu One as it lets me access all my Canonical stuff, and find it annoying to be able to enter it each time i want to buy anything. I don't want to change it to be easy either, as I don't want to put my access in risk.

Maybe we can use the phone security setting (passcode/password) to authenticate against unwanted purchases? (this would imply making mandatory the use of some sort of security in the phone for those people that want to be able to purchase stuff from the store)

UX Solution:

Once a user has entered their Ubuntu one password, there should be a time out feature, whereby the user will not need to enter their password again for 30 minutes (when the time out occurs).

If the user's phone is locked, then upon unlocking and using the Ubuntu store they will be required to enter their Ubuntu one password once again regardless of whether their 30 minutes are up or not.

NB: Time out should be set to 30 minutes.