Initial commit using Core's usermeta implementation as a template

From https://core.trac.wordpress.org/browser/trunk/src/wp-includes/session.php?rev=29635

wp-redis-session-storage.php

+<?php
+
+/**
+ * Meta-based user sessions token manager.
+ *
+ * @since 4.0.0
+ */
+class WP_Redis_Session_Storage extends WP_Session_Tokens {
+
+	/**
+	 * Get all sessions of a user.
+	 *
+	 * @since 4.0.0
+	 * @access protected
+	 *
+	 * @return array Sessions of a user.
+	 */
+	protected function get_sessions() {
+		$sessions = get_user_meta( $this->user_id, 'session_tokens', true );
+
+		if ( ! is_array( $sessions ) ) {
+			return array();
+		}
+
+		$sessions = array_map( array( $this, 'prepare_session' ), $sessions );
+		return array_filter( $sessions, array( $this, 'is_still_valid' ) );
+	}
+
+	/**
+	 * Converts an expiration to an array of session information.
+	 *
+	 * @param mixed $session Session or expiration.
+	 * @return array Session.
+	 */
+	protected function prepare_session( $session ) {
+		if ( is_int( $session ) ) {
+			return array( 'expiration' => $session );
+		}
+
+		return $session;
+	}
+
+	/**
+	 * Retrieve a session by its verifier (token hash).
+	 *
+	 * @since 4.0.0
+	 * @access protected
+	 *
+	 * @param string $verifier Verifier of the session to retrieve.
+	 * @return array|null The session, or null if it does not exist
+	 */
+	protected function get_session( $verifier ) {
+		$sessions = $this->get_sessions();
+
+		if ( isset( $sessions[ $verifier ] ) ) {
+			return $sessions[ $verifier ];
+		}
+
+		return null;
+	}
+
+	/**
+	 * Update a session by its verifier.
+	 *
+	 * @since 4.0.0
+	 * @access protected
+	 *
+	 * @param string $verifier Verifier of the session to update.
+	 * @param array  $session  Optional. Session. Omitting this argument destroys the session.
+	 */
+	protected function update_session( $verifier, $session = null ) {
+		$sessions = $this->get_sessions();
+
+		if ( $session ) {
+			$sessions[ $verifier ] = $session;
+		} else {
+			unset( $sessions[ $verifier ] );
+		}
+
+		$this->update_sessions( $sessions );
+	}
+
+	/**
+	 * Update a user's sessions in the usermeta table.
+	 *
+	 * @since 4.0.0
+	 * @access protected
+	 *
+	 * @param array $sessions Sessions.
+	 */
+	protected function update_sessions( $sessions ) {
+		if ( ! has_filter( 'attach_session_information' ) ) {
+			$sessions = wp_list_pluck( $sessions, 'expiration' );
+		}
+
+		if ( $sessions ) {
+			update_user_meta( $this->user_id, 'session_tokens', $sessions );
+		} else {
+			delete_user_meta( $this->user_id, 'session_tokens' );
+		}
+	}
+
+	/**
+	 * Destroy all session tokens for a user, except a single session passed.
+	 *
+	 * @since 4.0.0
+	 * @access protected
+	 *
+	 * @param string $verifier Verifier of the session to keep.
+	 */
+	protected function destroy_other_sessions( $verifier ) {
+		$session = $this->get_session( $verifier );
+		$this->update_sessions( array( $verifier => $session ) );
+	}
+
+	/**
+	 * Destroy all session tokens for a user.
+	 *
+	 * @since 4.0.0
+	 * @access protected
+	 */
+	protected function destroy_all_sessions() {
+		$this->update_sessions( array() );
+	}
+
+	/**
+	 * Destroy all session tokens for all users.
+	 *
+	 * @since 4.0.0
+	 * @access public
+	 * @static
+	 */
+	public static function drop_sessions() {
+		delete_metadata( 'user', false, 'session_tokens', false, true );
+	}
+}