Token encryption migration using attr_encrypted gem

Example token encryption migration

# Given mongoid Account model

class Account
  include Mongoid::Document
  
  field encrypted_token
  field token_version
  
  attr_encryptor :token, key: proc { |account| ENV["ACCOUNT_TOKEN_ENCRYPTION_KEY_V#{account.token_version}"] }, encode: true
end

# Steps to Migrate token to new encryption version
# 1. set new ENV variable (naming important)
ENV['ACCOUNT_TOKEN_VERSION2'] = 'new_encryption_key'

# 2. Update token_version and token
a = Account.new(_id: '5:1234', token: 'insta_token')
a.save
# => true
a.encrypted_token
# => "y5yjzWD34w2TKPAOd84G8w==\n"
a.token
# => "insta_token"
a.update_attributes(token_version: 2, token: a.token)
# => true
a.encrypted_token
# => "l3nk0xuoH9myvmVt2CwfUw==\n"
a.token
# => "insta_token"