Rails 3.x plugin to enhance Rails' session handling behavior.
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Copyright 2007-2017 t.e.morgan.
License: MIT

Updates/info: http://iprog.com/projects#limited_sessions
Source: https://github.com/zarqman/limited_sessions
Contact: tm@iprog.com

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 4+ extension to the (now separate) ActiveRecord Session Store to
    auto-cleanup stale session records.

Notes on Rails and Rack versions:
  The middleware should be compatible with any framework using a recent
  version of Rack. It was tested with Rack 1.5 on Rails 4.2 and Rack 2.0 on
  Rails 5.0 and 5.1.
  The ActiveRecord Session Store extension requires Rails 4+ and the now
  separate activerecord-session_store gem:
    gem 'activerecord-session_store'
  activerecord-session_store must be *before* limited_sessions in your Gemfile
  in order for limited_sessions to auto-detect it.

  The extension has been tested with the following combinations:
  * Rails 4.2 + activerecord-session_store 0.1.2
  * Rails 5.0 + activerecord-session_store 1.0.0
  * Rails 5.1 + activerecord-session_store 1.1.0

Upgrading from previous versions:
  Other than possibly requiring the activerecord-session_store gem as noted
  above, no changes are required upgrading from limited_sessions 3.x to 4.0.

  If upgrading from limited_sessions v2.x, please review the upgrade notes from
  limited_sessions 3.x or build a new configuration using the instructions

  * 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

  * Rack and any Rack-compatible app (including Rails 4 or 5)
  * Utilizing Rack's (or Rails') sessions support
  * 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

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

  gem 'limited_sessions', '~> 4.0'

  Rack Middleware with Rails
    1. Update your config/initializers/session_store.rb and append the

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

    2. Configuration options.
       The example above shows both configuration options. You may include
       both, one, 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
    1. In your config.ru, add the following *after* the middleware that handles
       your sessions.

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

    2. See #2 above, under Rack Middleware with Rails, for Configuration options.       

  ActionRecord Session Store
    1. 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'.

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

       <YourApp>::Application.config.session_store :active_record_store
       ActionDispatch::Session::ActiveRecordStore.session_class = LimitedSessions::SelfCleaningSession

    3. 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 about 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. 0 will 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 this was 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, the 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

Other 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
    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 halves 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.

  Is the AR enhancement compatible with the legacy 'sessid' column?
    No. Please rename that column to 'session_id'.

Other Notes:
  This version has been tested on Rack 1.5-2.0 and Rails 4.2-5.1. It should be
  compatible with a broad spectrum of data and session stores. If you find a
  bug, I'd love to hear about it -- preferably via a new issue on GitHub (bonus
  points for a pull request). Likewise, give me a shout if you have a suggestion
  or just want to tell me that it works. Thanks for checking limited_sessions
      --t (tm@iprog.com; https://iprog.com/)