The App Store app update kept asking for Yahoo password
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.