https://stackoverflow.com/questions/31715385/single-sign-out-from-multiple-applications-from-doorkeeper-provider?noredirect=1#comment51735602_31715385

application controller sample code.rb

session = {}

# see https://github.com/mperham/dalli
def common_cache
  @common_cache ||= Dalli::Client.new('localhost:11211', { :namespace => "all_apps", :compress => true })
end

def session.[] (arg)
  if arg.to_s == 'access_token'
    @access_token ||= common_cache.get("sessions/#{self[:user_id]}")
  else
    super(arg)
  end 
end

def session.[]= (arg, value)
  if arg.to_s == 'access_token'
    binding.pry
    common_cache.set("sessions/#{self[:user_id]}", value)
    @access_token = value
  else
    super(arg, value)
  end 
end


session[:user_id] = 23323
session[:access_token] = 'rkhuhwiwuhiewrhwekjnewu4yuin'

puts session[:user_id] # returns from session
puts session[:access_token] # returns from memcache

puts session