1__.env

DWOLLA_ACCOUNT_ID= # your Dwolla account id, e.g. "875ab9e7-e211-472c-a7b5-af6c798b041d"
DWOLLA_CLIENT_ID= # your App's consumer key
DWOLLA_CLIENT_SECRET= # your App's consumer secret
DWOLLA_ACCOUNT_REFRESH_TOKEN= # refresh token generated on dwolla.com
SECRET_KEY= # a secret used for encrypting oauth tokens

2__Gemfile

gem "attr_encrypted", "~> 3.0.0"

3__config--initializers--inflectors.rb

ActiveSupport::Inflector.inflections(:en) do |inflect|
  # If you don't add this, Rails will name your model TokenDatum
  # when you run the command in generate_model.sh
  inflect.irregular "data", "data"
end

4__generate_model.sh

rails generate model TokenData \
  encrypted_access_token \
  encrypted_access_token_iv \
  encrypted_refresh_token \
  encrypted_refresh_token_iv \
  expires_in:integer \
  scope \
  account_id

5__app--models--token_data.rb

class TokenData < ActiveRecord::Base
  DESIRED_FRESHNESS = 1.minute
  SECRET_KEY = ENV["SECRET_KEY"]

  attr_encrypted :access_token, key: SECRET_KEY
  attr_encrypted :refresh_token, key: SECRET_KEY

  # look in the token_data table for the most recent token matching the given criteria
  # if one does not exist throw an `ActiveRecord::RecordNotFound` error
  # if one does exist convert the `TokenData` to a fresh `DwollaV2::Token` (see `#to_fresh_token`)
  def self.fresh_token_by! criteria
    where(criteria)
      .order(created_at: :desc)
      .first!
      .to_fresh_token
  end

  def to_fresh_token
    if expired?
      # if the token data is expired either refresh the token (account token) or get a new token (app token)
      account_id? \
        ? $dwolla.auths.refresh(self) \
        : $dwolla.auths.client
    else
      # if the token is not expired just convert it to a DwollaV2::Token
      $dwolla.tokens.new(self)
    end
  end

  private

  def expired?
    created_at < Time.now.utc - expires_in.seconds + DESIRED_FRESHNESS
  end
end

6__config--initializers--dwolla.rb

$dwolla = DwollaV2::Client.new(id: ENV["DWOLLA_CLIENT_ID"], secret: ENV["DWOLLA_CLIENT_SECRET"]) do |config|
  # whenever a token is granted, save it to ActiveRecord
  config.on_grant do |token|
    TokenData.create! token
  end
end

# create an application token if one doesn't already exist
begin
  TokenData.fresh_token_by! account_id: nil
rescue ActiveRecord::RecordNotFound => e
  $dwolla.auths.client # this gets saved in our on_grant callback
end

# create an account token if one doesn't already exist
begin
  TokenData.fresh_token_by! account_id: ENV["DWOLLA_ACCOUNT_ID"]
rescue ActiveRecord::RecordNotFound => e
  TokenData.create! account_id: ENV["DWOLLA_ACCOUNT_ID"],
                    refresh_token: ENV["DWOLLA_ACCOUNT_REFRESH_TOKEN"],
                    expires_in: -1
end

6__token_concern.rb

module TokenConcern
  extend ActiveSupport::Concern

  private

  def account_token
    @account_token ||= TokenData.fresh_token_by! account_id: ENV["DWOLLA_ACCOUNT_ID"]
  end

  def app_token
    @app_token ||= TokenData.fresh_token_by! account_id: nil
  end
end

7__foo.rb

class Foo
  include TokenConcern

  def bar
    app_token.get "events"
  end

  def baz
    account_token.get "customers"
  end
end

Thank you for great gist !