Mac OS Finder and iCloud may start prompting you again and again for your AppleID/iCloud password, leaving you confused as to why it keeps asking for it — even though you are certain that you entered your password correctly the first time it asked.
iCloud has a number of different components and services and features, and depending on which of those components you are utilizing or have switched on in Mac OS System Preferences, you will be prompted to input your password one time for each one of those components you are utilizing.
If you are prompted for your password at least two or more times after you input it the first time, this means you have entered the password correctly at the first prompt — so continue to input the same password if iCloud continues to prompt you to do so.
A common confusion among users of iCloud is that upon being asked for their password a second time, the user may immediately think that they have entered the wrong password at the first prompt. So they may try a different password the second time, when in fact they had the password correct the first time they entered it.
Too many login attempts with the wrong password will result in the user being locked out of their iCloud account, and thus required to go to iforgot.apple.com to change their AppleID password -- and hope they can remember the answers to the security questions they originally set up.
When you have entered your password one time for each component and feature that iCloud needs to re-authenticate, the Mac will cease the prompts, and you should then observe that all of your iCloud features and services are switched on and functioning as they should be.
This is likely to be triggered by one or more of the following circumstances:
- You have changed the password for your AppleID
- You have been signed out of iCloud on a Mac and want to sign into iCloud again on that same Mac
- You have upgraded your Mac OS system software (i.e. 10.11 to 10.12)
- You have just installed and applied a Mac OS incremental update from the Mac App Store (i.e. 10.12.3 to 10.12.4)