An example of auto expiring user tokens

User.rb

require 'digest/md5'

class User
  attr_accessor :name, :token_valid_for
  attr_reader :pwd_hash


  def initialize(name, pwd)
    self.name = name
    self.password = pwd
    self.token_valid_for = 7
  end


  def password=(pwd)
    @pwd_hash = digest(pwd)
  end


  def api_token
    digest(name + expirable_salt + time_dependent_salt)
  end



  private


  def digest(string)
    Digest::MD5.hexdigest string
  end


  def expirable_salt
    pwd_hash[0,10]
  end


  def time_dependent_salt
    t = Time.now
    t.year.to_s + (t.yday / token_valid_for).to_s
  end

end