How to fix the ERROR 1698 (28000): Access denied for user 'root'@'localhost'

After upgrading from MySQL version 5.5 to 5.7, whenever I tried to log in to the database as non sudo user it throws following error. But I was able to log into the system as sudo user without any issues.

firzhan@firzhan-wso2:/etc/mysql$ mysql -u root -padmin 

mysql: [Warning] Using a password on the command line interface can be insecure.

ERROR 1698 (28000): Access denied for user 'root'@'localhost'

I followed following steps to do a quick fix

• First connect to the mysql as sudo user.
• Check the users presently available in the databases's user table.

1. SELECT User,Host FROM mysql.user;
   +------------------+-----------+
   | User             | Host      |
   +------------------+-----------+
   | admin            | localhost |
   | root             |    *      |
   | root             | %         |
   | mysql.sys        | localhost |
   | root             | localhost |

• Delete all the entries/accounts related to root user.

• mysql> DROP USER 'root'@'localhost';
  Query OK, 0 rows affected (0,00 sec)
  

  mysql> DROP USER 'root'@'*';
  Query OK, 0 rows affected (0,00 sec)

  mysql> DROP USER '%';
  Query OK, 0 rows affected (0,00 sec)

• Again insert an entry for root user in the table.

• mysql> CREATE USER 'root'@'%' IDENTIFIED BY '';
  Query OK, 0 rows affected (0,00 sec)

• Grant relevant permissions for that particular user of the database and make sure to flush the privileges.

• mysql> GRANT ALL PRIVILEGES ON *.* TO 'root'@'%';
  Query OK, 0 rows affected (0,00 sec)
  
  mysql> FLUSH PRIVILEGES;
  Query OK, 0 rows affected (0,01 sec)

• Exit and try to reconnect to the terminal without sudo.