How to use own CMS login as WordPress login

Solution:

For that above requirement, you need matching username/password with WP site.

When users are trying to register into your site use wp_create_user( $username, $password, $email ); and when users are logging into your site you can use following code

$creds = array(
    'user_login'    => 'example',
    'user_password' => 'plaintextpw',
    'remember'      => true
);

$user = wp_signon( $creds, false );