Retrieves a user row based on password reset key and login.

A key is considered ‘expired’ if it exactly matches the value of the
user_activation_key field, rather than being matched after going through the
hashing process. This field is now hashed; old values are no longer accepted
but have a different WP_Error code so good user feedback can be provided.

function check_password_reset_key( $key, $login ) {
	global $wpdb, $wp_hasher;

	$key = preg_replace( '/[^a-z0-9]/i', '', $key );

	if ( empty( $key ) || ! is_string( $key ) ) {
		return new WP_Error( 'invalid_key', __( 'Invalid key.' ) );
	}

	if ( empty( $login ) || ! is_string( $login ) ) {
		return new WP_Error( 'invalid_key', __( 'Invalid key.' ) );
	}

	$user = get_user_by( 'login', $login );

	if ( ! $user ) {
		return new WP_Error( 'invalid_key', __( 'Invalid key.' ) );
	}

	if ( empty( $wp_hasher ) ) {
		require_once ABSPATH . WPINC . '/class-phpass.php';
		$wp_hasher = new PasswordHash( 8, true );
	}

	/**
	 * Filters the expiration time of password reset keys.
	 *
	 * @since 4.3.0
	 *
	 * @param int $expiration The expiration time in seconds.
	 */
	$expiration_duration = apply_filters( 'password_reset_expiration', DAY_IN_SECONDS );

	if ( false !== strpos( $user->user_activation_key, ':' ) ) {
		list( $pass_request_time, $pass_key ) = explode( ':', $user->user_activation_key, 2 );
		$expiration_time                      = $pass_request_time + $expiration_duration;
	} else {
		$pass_key        = $user->user_activation_key;
		$expiration_time = false;
	}

	if ( ! $pass_key ) {
		return new WP_Error( 'invalid_key', __( 'Invalid key.' ) );
	}

	$hash_is_correct = $wp_hasher->CheckPassword( $key, $pass_key );

	if ( $hash_is_correct && $expiration_time && time() user_activation_key, $key ) || ( $hash_is_correct && ! $expiration_time ) ) {
		$return  = new WP_Error( 'expired_key', __( 'Invalid key.' ) );
		$user_id = $user->ID;

		/**
		 * Filters the return value of check_password_reset_key() when an
		 * old-style key is used.
		 *
		 * @since 3.7.0 Previously plain-text keys were stored in the database.
		 * @since 4.3.0 Previously key hashes were stored without an expiration time.
		 *
		 * @param WP_Error $return  A WP_Error object denoting an expired key.
		 *                          Return a WP_User object to validate the key.
		 * @param int      $user_id The matched user ID.
		 */
		return apply_filters( 'password_reset_key_expired', $return, $user_id );
	}

	return new WP_Error( 'invalid_key', __( 'Invalid key.' ) );
}