LimitedSessions

LimitedSessions provides two distinct features, each in a separate part:

Rack-compatible middleware that expires sessions based on inactivity or maximum session length. The middleware supports any session storage type, including cookies, Redis, ActiveRecord, etc.
Rails extension to the (now separate) ActiveRecord Session Store to auto-cleanup stale session records.

Features

For all session stores:
- Configurable session expiry time (eg: 2 hours from last page access)
- Optional hard maximum limit from beginning of session (eg: 24 hours)
When using the ActiveRecord Session Store:
- DB-based handling of session expiry (activity and hard limits) instead of by session paramters
- Auto-cleaning of expired session records

Requirements

Rack and any Rack-compatible app (including Rails)
Utilizing Rack's (or Rails') sessions
For ActiveRecord session enhancements:
- Must be using the standard ActiveRecord::SessionStore (ActionDispatch::Session::ActiveRecordStore.session_store = :active_record_store)
- Ensure your sessions table has an updated_at column
- If using hard session limits, a created_at column is needed too

Compatibility

The middleware should be compatible with any framework using a recent version of Rack. It has been tested with Rack 2-3 and Rails 5.2-7.1.

The optional ActiveRecord Session Store extension requires Rails.

If using Rack < 2.0.9 or Rails < 5.2, use LimitedSessions 4.x.

Upgrading

No changes are required to upgrade from LimitedSessions 4.x to 5.0.

Upgrading activerecord-session_store from 1.x to 2.x may require changes. See its own upgrade instructions.

Installation

Add this gem to your Gemfile or otherwise make it available to your app. Then, configure as required.

gem 'limited_sessions', '~> 5'

If storing sessions in the DB using ActiveRecord with AR Session Store:

gem 'activerecord-session_store'
gem 'limited_sessions', '~> 5'

activerecord-session_store must be loaded first in order for limited_sessions to properly detect it.

Configuration

Rack Middleware with Rails

Add/update config/initializers/session_store.rb and append the following:

config.middleware.insert_after ActionDispatch::Flash, LimitedSessions::Expiry, \
  recent_activity: 2.hours, max_session: 24.hours

Configuration options.

The example above shows both configuration options. You may include one, both, or none.

Session activity timeout

Example: recent_activity: 2.hours By default, the session activity timeout is disabled (nil).

Maximum session length

Example: max_session: 24.hours By default, the maximum session length is disabled (nil).

Rack Middleware apart from Rails

In config.ru, add the following after the middleware that handles your sessions.

use LimitedSessions::Expiry, recent_activity: 2.hours, max_session: 24.hours

For configuration options, see #2 above, under Rack Middleware with Rails.

ActionRecord Session Store extension

If you don't already have an updated_at column on your sessions table, create a migration and add it. If you plan to use the hard session limit feature, you'll also need to add created_at.

Tell Rails to use your the new session store. Change config/initializers/session_store.rb to reflect the following:

Rails.application.config.session_store :active_record_store
ActionDispatch::Session::ActiveRecordStore.session_class = LimitedSessions::SelfCleaningSession

Configuration options.

Each of the following options should also be added to your initializer file from step 2.

Self-cleaning

By default, SelfCleaningSession will clean the sessions table every 1000 page views. Technically, it's a 1 in 1000 chance on each page. For most sites this is good. Higher traffic sites may want to increase it to 10000 or more. Set to 0 to disable self-cleaning.
```
LimitedSessions::SelfCleaningSession.self_clean_sessions = 1000
```
Session activity timeout

The default session activity timeout is 2 hours. This uses the updated_at column which will be updated on every page load.

This can also be disabled by setting to nil. However, the updated_at column is still required for self-cleaning and will effectively function as if set to 1.week. If you really want it longer, set it to 1.year or something.
```
LimitedSessions::SelfCleaningSession.recent_activity = 2.hours
```
Maximum session length

By default, maximum session length handling is disabled. When enabled, it uses the created_at column to do its work.

A value of nil disables this feature and created_at does not need to exist in this case.
```
LimitedSessions::SelfCleaningSession.max_session = 12.hours
```

Questions

Do I need both the middleware and the ActiveRecord Session Store?

No. While it should work, it is not necessary to use both the middleware and the ActiveRecord Session Store. If you are storing sessions via AR, then use the ActiveRecord Session Store. If you are storing sessions any other way, then use the middleware.
I'm storing sessions in {Memcache, Redis, etc.} and they auto-expire sessions. Do I need this?

Maybe, maybe not. Normally, that auto-expire period is equivalent to LimitedSessions' :recent_activity. If that's all you want, then you don't need this. However, if you'd also like to put a maximum cap on session length, regardless of activity, then LimitedSessions' :max_session feature will still be useful.
Can I use the middleware with ActiveRecord instead of the ActionRecord Session Store enhancement?

Yes. Session expiry (recent activity and max session length) should work fine in this circumstance. The only thing you won't get is self-cleaning of the AR sessions table.
How are session expiry times tracked?

The middleware adds one or two keys to the session data: :last_visit and/or :first_visit.

The AR enhancement uses updated_at and possibly created_at.
How is this different from using the session cookie's own expires= value?

The cookie's own value puts the trust in the client to self-expire. If you really want to control session lengths, then you need to manage the values on the application side. LimitedSessions is fully compatible with the cookie's expires= value, however, and the two can be used together.
What's the difference between :recent_activity and :max_session?

Recent activity requires regular access on your site. If it's set to 15 minutes, then a page must be loaded at least once every 15 minutes.

Max session is a cap on the session from the very beginning. If it's set to 12 hours, then even if a user is accessing the page constantly, and not triggering the recent activity timeout, after 12 hours their session would be reset anyway.
What are the security implications of using LimitedSessions?

LimitedSessions enhances security by reducing risk of session cookie replay attacks. The specifics will depend on what cookie store you're using.

For Rails' default cookie store, :max_session handling is perhaps most valuable as it guarantees an end to the session. Rails' default behavior allows a session to last for an infinite time. If a cookie is somehow exposed, the holder of the cookie has an open-ended session. Note that signing and/or encryption do not mitigate this.

For any session store that uses a server-side database (AR, memcache, Redis, etc.), at least the user can formally logout and terminate the session. Auto-expiring sessions (memcache, Redis, AR w/SelfCleaningSession, etc.) will also expire if allowed to, but can also be maintained perpetually by ongoing access.

Since the cookie store doesn't expire ever, :recent_activity addresses this by making sessions expire similarly to if memcache, Redis, or something similar was being used.

It is recommended to use both aspects of LimitedSessions for best security.
What are the performance implications of using LimitedSessions?

The middleware should have minimal impact.

The AR enhancement should result in an overall net gain in performance as the size of the AR sessions table will be kept to a smaller size. The 1 in 1000 hit (or whatever you've configured it to) may be slightly slower while the database cleanup is in progress.

Contributing

Fork it ( https://github.com/zarqman/limited_sessions/fork )
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request

License

MIT

zarqman/limited_sessions