The App Store app update kept asking for Yahoo password I was trying to update YouTube on an iPhone 5S with iOS 7.0 but it asked me for Yahoo password, not iCloud password.

How am I supposed to solve this problem?
The app store dialog that is titled "Sign in to iTunes Store" is worded slightly ambiguously.  The last sentence reads (for example:) `Enter the password for "youremail@yahoo.com".

You are not being asked here for the password to your yahoo account.  You are being asked for the password for your appleId that uses "youremail@yahoo.com" as it's username.