gistfile1.rb

# The idea here is that if any of the three tokens are not already
# set, then they should be generated. In order to generate one, it
# must be unique.
def generate_tokens!
  [ :code, :access_token, :refresh_token ].each do |attr|
    next if send(attr)
    send "#{attr}=", tokenize(attr)
  end
end

def tokenize(attr)
  token = loop do
    t = SecureRandom.hex(16)
    break t unless self.class.exists?(attr => t)
  end
end