Begin keeping record of user sessions in reds.

services/web/app/coffee/Features/Authentication/AuthenticationController.coffee

@@ -9,6 +9,7 @@ Url = require("url")
 Settings = require "settings-sharelatex"
 basicAuth = require('basic-auth-connect')
 UserHandler = require("../User/UserHandler")
+UserSessionsManager = require("../User/UserSessionsManager")
 
 module.exports = AuthenticationController =
 	login: (req, res, next = (error) ->) ->
@@ -141,4 +142,6 @@ module.exports = AuthenticationController =
 			req.session[key] = value
 
 		req.session.user = lightUser
+
+		UserSessionsManager.onLogin(user, req.sessionID, () ->)
 		callback()

services/web/app/coffee/Features/User/UserController.coffee

@@ -8,6 +8,7 @@ logger = require("logger-sharelatex")
 metrics = require("../../infrastructure/Metrics")
 Url = require("url")
 AuthenticationManager = require("../Authentication/AuthenticationManager")
+UserSessionsManager = require("./UserSessionsManager")
 UserUpdater = require("./UserUpdater")
 settings = require "settings-sharelatex"
 
@@ -81,9 +82,12 @@ module.exports = UserController =
 	logout : (req, res)->
 		metrics.inc "user.logout"
 		logger.log user: req?.session?.user, "logging out"
+		sessionId = "#{req.sessionID}"
+		user = req?.session?.user
 		req.session.destroy (err)->
 			if err
 				logger.err err: err, 'error destorying session'
+			UserSessionsManager.onLogout(user, sessionId)
 			res.redirect '/login'
 
 	register : (req, res, next = (error) ->)->

services/web/app/coffee/Features/User/UserSessionsManager.coffee

@@ -0,0 +1,31 @@
+Settings = require('settings-sharelatex')
+redis = require('redis-sharelatex')
+rclient = redis.createClient(Settings.redis.web)
+logger = require("logger-sharelatex")
+
+module.exports = UserSessionsManager =
+
+	_sessionSetKey: (user) ->
+		console.log ">>", user
+		return "UserSessions:#{user._id}"
+
+	onLogin: (user, sessionId, callback=(err)-> ) ->
+		logger.log {user_id: user._id, sessionId}, "onLogin handler"
+		sessionSetKey = UserSessionsManager._sessionSetKey(user)
+		rclient.sadd sessionSetKey, sessionId, (err, response) ->
+			if err
+				logger.err {err, user_id: user._id, sessionId}, "error while adding session key to UserSessions set"
+				return callback(err)
+			callback()
+
+	onLogout: (user, sessionId, callback=(err)-> ) ->
+		logger.log {user_id: user._id, sessionId}, "onLogout handler"
+		if !user
+			logger.log {sessionId}, "no user, for some reason"
+			return callback()
+		sessionSetKey = UserSessionsManager._sessionSetKey(user)
+		rclient.srem sessionSetKey, sessionId, (err, response) ->
+			if err
+				logger.err {err, user_id: user._id, sessionId}, "error while removing session key from UserSessions set"
+				return callback(err)
+			callback()