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The user  table plugin  and authentication_string  columns store authentication plugin and credential information. 

The server uses the plugin named in the plugin  column of an account row to authenticate connection attempts for the account. 

The plugin  column must be nonempty. At startup, and at runtime when FLUSH PRIVILEGES  is executed, the server checks user  table rows. For any row with an empty plugin  column, the server writes a warning to the error log of this form: 

[Warning] User entry ’ user_name ’@’ host_name ’ has an empty plugin value. The user will be ignored and no one can login with this user anymore. 

To assign a plugin to an account that is missing one, use the ALTER USER  statement. 

The password_expired  column permits DBAs to expire account passwords and require users to reset their password. The default password_expired  value is ’N’ , but can be set to ’Y’  with the ALTER USER  statement. After an account’s password has been expired, all operations performed by the account in subsequent connections to the server result in an error until the user issues an ALTER USER  statement to establish a new account password. 

