How this can help? Please clarify your idea
Well, you could copy the password check function from wordpress into that hook, effectively keeping the same hash. Therefore users would be able to keep their passwords.
You can get this class overhere: https://github.com/WordPress/WordPress/blob/master/wp-includes/class-phpass.php
And the function looks as follows:
function wp_check_password($password, $hash, $user_id = '') {
global $wp_hasher;
// If the hash is still md5...
if ( strlen($hash) <= 32 ) {
$check = hash_equals( $hash, md5( $password ) );
if ( $check && $user_id ) {
// Rehash using new hash.
wp_set_password($password, $user_id);
$hash = wp_hash_password($password);
}
/**
* Filters whether the plaintext password matches the encrypted password.
*
* @since 2.5.0
*
* @param bool $check Whether the passwords match.
* @param string $password The plaintext password.
* @param string $hash The hashed password.
* @param string|int $user_id User ID. Can be empty.
*/
return apply_filters( 'check_password', $check, $password, $hash, $user_id );
}
// If the stored hash is longer than an MD5, presume the
// new style phpass portable hash.
if ( empty($wp_hasher) ) {
require_once( ABSPATH . WPINC . '/class-phpass.php');
// By default, use the portable hash from phpass
$wp_hasher = new PasswordHash(8, true);
}
$check = $wp_hasher->CheckPassword($password, $hash);
/** This filter is documented in wp-includes/pluggable.php */
return apply_filters( 'check_password', $check, $password, $hash, $user_id );
}