Stop "...wants to use keychain" password prompts
Your Mac keeps asking for the login keychain password and this means 
The password of your macOS user account might not match the password of your login keychain. 

It might also tell you that the system was unable to unlock your login keychain. That's because your login keychain is still using another password.

If you don't know your this password, the solution is to create a new login keychain or reset to default.


Open Keychain Access, which is in the Utilities folder within the Applications folder.or Launchpad > Utilities > Keychain Access
From the Keychain Access menu, choose Preferences.
Click General, then click Reset My Default Keychain.
Add your account login password.
Quit Keychain Access then Restart your computer.



  From Apple support
  
  If you know your old password, use that password to update your existing login keychain:
  
  
  Open the Keychain Access app, which is in the the Utilities folder of your Applications folder. or Launchpad > Utilities > Keychain Access
  From the Edit menu, choose “Change Password for Keychain 'login.'”
  Enter the old password of your user account in the Current Password field. This is the password you were using before the password was reset.
  Enter the new password of your user account in the New Password field. This is the password you're now using to log in to your Mac. Enter the same password in the Verify field.
  Click OK when done, then quit Keychain Access.