php mysqli_connect: authentication method unknown to the client [caching_sha2_password]

I am using php mysqli_connect for login to a MySQL database (all on localhost)

<?php
//DEFINE ('DB_USER', 'user2');
//DEFINE ('DB_PASSWORD', 'pass2');
DEFINE ('DB_USER', 'user1');
DEFINE ('DB_PASSWORD', 'pass1');
DEFINE ('DB_HOST', '127.0.0.1');
DEFINE ('DB_NAME', 'dbname');

$dbc = mysqli_connect(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);

if(!$dbc){
    die('error connecting to database');    
}
?>

this is the mysql.user table:

MySQL Server ini File:

[mysqld]
# The default authentication plugin to be used when connecting to the server
default_authentication_plugin=caching_sha2_password
#default_authentication_plugin=mysql_native_password

with caching_sha2_password in the MySQL Server ini file, it's not possible at all to login with user1 or user2;

error: mysqli_connect(): The server requested authentication method unknown to the client [caching_sha2_password] in...

with mysql_native_password in the MySQL Server ini file, it's possible to login with user1, but with user2, same error;

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how can I login using caching_sha2_password on the mySql Server?

As of PHP 7.4, this is no longer an issue. Support for caching_sha2 authentication method has been added to mysqlnd.

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Currently, PHP mysqli extension do not support new caching_sha2 authentication feature. You have to wait until they release an update.

Check related post from MySQL developers: https://mysqlserverteam.com/upgrading-to-mysql-8-0-default-authentication-plugin-considerations/

They didn't mention PDO, maybe you should try to connect with PDO.