Keychain is a built-in feature with with Mac to manage passwords. Any password you've saved in your Apple computer, whether it be for system management, wi-fi access, or your email, is saved in Keychain, along with security certificates for any website you visit. Your passwords are physically stored in a variety of locations, depending on the associated program and function, but you can access and disable all automatic logins and prompts through Keychain Access. You can also delete specific passwords and keep others. Two solutions to Keychain issues are detailed below.
Find Keychain Access in your Utilities folder (Macintosh HD/Applications/Utilities/Keychain Access.app) and open the application.
Solution one: Disable Keychain at login by changing your Keychain password. If your issue is persistent Keychain popups, you can create a separate login for Keychain. The default password for Keychain is your system password, which means that you are automatically logged in to Keychain each time your start your computer. Changing your password will stop Keychain from operating automatically, thereby disabling it.
Go to "Edit" in your Keychain Access toolbar and select "Change Password for Keychain 'login'..." from that menu. Enter your old (system) password and your new Keychain password. From this point on, you will have to manually login to Keychain Access if you need the information stored there, but Keychain will not talk to your applications or open annoying popups.
Solution two: From Keychain Access, click "login" on the Keychains menu to your left. A list of locations and passwords will appear.
Select "Passwords" from the Category menu beneath they Keychains menu to filter and limit your results to passwords if your list is extensive.
If you want to disable all logins, autofills, and passwords, select every item on the list and press the "delete" key. Any item you delete will be gone forever, so be careful here.
To delete only certain passwords (to disable automatic email login when you plan on sharing your computer or account, for example), find the item in the list, highlight it, and delete it.
Add keychain to your dock for easy access if you change the Keychain password. You might need to pop into Keychain Access more frequently after doing this.
You can always change your Keychain password back to the system password later to restore the original functionality.
Any password you delete will be permanently deleted.