Ruby gem to implement Google's MFA authenticator
Ruby
Latest commit 54b0eaa Oct 31, 2017 @jaredonline jaredonline Bump version

README.md

GoogleAuthenticatorRails

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Rails (ActiveRecord) integration with the Google Authenticator apps for Android and the iPhone. Uses the Authlogic style for cookie management.

Installation

Add this line to your application's Gemfile:

gem 'google-authenticator-rails'

And then execute:

$ bundle

Or install it yourself as:

$ gem install google-authenticator-rails

Usage

Example:

class User
  acts_as_google_authenticated
end

@user = User.new
@user.set_google_secret           # => true
@user.google_qr_uri               # => http://path.to.google/qr?with=params
@user.google_authentic?(123456)   # => true

Google Labels

When setting up an account with GoogleAuthenticatorRails you need to provide a label for that account (to distinguish it from other accounts).

GoogleAuthenticatorRails allows you to customize how the record will create that label. There are three options:

  • The default just uses the column email on the model
  • You can specify a custom column with the :column_name option
  • You can specify a custom method via a symbol or a proc

Example:

class User
  acts_as_google_authenticated :column => :user_name
end

@user = User.new(:user_name => "ted")
@user.google_label                      # => "ted"

class User
	acts_as_google_authenticated :method => :user_name_with_label

	def user_name_with_label
	  "#{user_name}@example.com"
	end
end

@user = User.new(:user_name => "ted")
@user.google_label                    # => "ted@example.com"

class User
	acts_as_google_authenticated :method => Proc.new { |user| user.user_name_with_label.upcase }

	def user_name_with_label
	  "#{user_name}@example.com"
	end
end

@user = User.new(:user_name => "ted")
@user.google_label                    # => "TED@EXAMPLE.COM"

Here's what the labels look like in Google Authenticator for iPhone:

iPhone Label Screenshot

Google Secret

The "google secret" is where GoogleAuthenticatorRails stores the secret token used to generate the MFA code.

You can also specify a column for storing the google secret. The default is google_secret.

Example

class User
	acts_as_google_authenticated :google_secret_column => :mfa_secret
end

@user = User.new
@user.set_google_secret
@user.mfa_secret 		 # => "56ahi483"

Drift

You can specify a custom drift value. Drift is the number of seconds that the client and server are allowed to drift apart. Default value is 5 seconds.

class User
  act_as_google_authenticated :drift => 31
end

Lookup Token

You can also specify which column the appropriate MfaSession subclass should use to look up the record:

Example

class User
  acts_as_google_authenticated :lookup_token => :salt
end

The above will cause the UserMfaSession class to call User.where(:salt => cookie_salt) or User.scoped(:conditions => { :salt => cookie_salt }) to find the appropriate record.

A note about record lookup

GoogleAuthenticatorRails makes one very large assumption when attempting to lookup a record. If your MfaSession subclass is named UserMfaSession it assumes you're trying to lookup a User record. Currently, there is no way to configure this, so if you're trying to lookup a VeryLongModelNameForUser you'll need to name your MfaSession subclass VeryLongModelNameForUserMfaSession.

For example:

# app/models/user.rb
class User < ActiveRecord::Base
  acts_as_google_authentic
end

# app/models/user_mfa_session.rb
class UserMfaSession < GoogleAuthenticatorRails::Session::Base
end

A note about cookie creation and Session::Persistence::TokenNotFound

GoogleAuthenticatorRails looks up the record based on the cookie created when you call MfaSession#create. The #create method looks into the record class (in our example, User) and looks at the configured :lookup_token option. It uses that option to save two pieces of information into the cookie, the id of the record and the token, which defaults to persistence_token. persistence_token is what Authlogic uses, which this gem was originally designed to work with.

This can cause a lot of headaches if the model isn't configured correctly, and will cause a GoogleAuthenticatorRails::Session::Persistence::TokenNotFound error.

This error appears for one of three reasons:

  1. user is nil
  2. user doesn't respond to :persistence_token
  3. user.persistence_token is blank

For example:

# app/models/user.rb
class User < ActiveRecord::Base
  acts_as_google_authentic
end

# Model has attributes:
# id:   integer
# name: string
# salt: string

# app/models/user_mfa_session.rb
class UserMfaSession < GoogleAuthenticatorRails::Session::Base
end

# app/controllers/mfa_session_controller.rb
class MfaSessionController < ApplicationController
  def create
    UserMfaSession.create(user) # => Error: GoogleAuthenticatorRails::Session::Persistence::TokenNotFound
  end
end

The above example will fail because the User class doesn't have a persistence_token method. The fix for this is to configure actions_as_google_authentic to use the right column:

# app/models/user.rb
class User < ActiveRecord::Base
  acts_as_google_authentic :lookup_token => :salt
end

# Model has attributes:
# id:   integer
# name: string
# salt: string

# app/models/user_mfa_session.rb
class UserMfaSession < GoogleAuthenticatorRails::Session::Base
end

# app/controllers/mfa_session_controller.rb
def class MfaSessionController < ApplicationController
  def create
    UserMfaSession.create(user)
  end
end

This call to #create will succeed (as long as user.salt is not nil).

Issuer

You can also specify a name for the 'issuer' (the name of the website) where the user is using this token:

Example

class User
  acts_as_google_authenticated :issuer => 'example.com'
end

This way your user will have the name of your site at the authenticator card besides the current token.

Here's what the issuers look like in Google Authenticator for iPhone:

iPhone Label Screenshot

Sample Rails Setup

This is a very rough outline of how GoogleAuthenticatorRails is meant to manage the sessions and cookies for a Rails app.

# Gemfile

gem 'rails'
gem 'google-authenticator-rails'

First add a field to your user model to hold the Google token.

class AddGoogleSecretToUser < ActiveRecord::Migration
  def change
    add_column :users, :google_secret, :string
  end
end
# app/models/users.rb

class User < ActiveRecord::Base
  acts_as_google_authenticated
end

If you want to authenticate based on a model called User, then you should name your session object UserMfaSession.

# app/models/user_mfa_session.rb

class UserMfaSession <  GoogleAuthenticatorRails::Session::Base
  # no real code needed here
end
# app/controllers/user_mfa_session_controller.rb

class UserMfaSessionController < ApplicationController

  def new
    # load your view
  end

  def create
    user = current_user # grab your currently logged in user
    if user.google_authentic?(params[:mfa_code])
      UserMfaSession.create(user)
      redirect_to root_path
    else
      flash[:error] = "Wrong code"
      render :new
    end
  end

end
# app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  before_filter :check_mfa

  private
  def check_mfa
     if !(user_mfa_session = UserMfaSession.find) && (user_mfa_session ? user_mfa_session.record == current_user : !user_mfa_session)
      redirect_to new_user_mfa_session_path
    end
  end
end

Cookie options

You can configure the MfaSession cookie by creating an initializer:

# config/initializers/google_authenticator_rails.rb

# The cookie normally expires in 24 hours, you can change this to 1 month
GoogleAuthenticatorRails.time_until_expiration = 1.month

# You can override the suffix of the cookie's key, by default this is mfa_credentials
GoogleAuthenticatorRails.cookie_key_suffix = 'mfa_credentials'

# Rails offers a few more cookie options, by default only :httponly is turned on, you can change it to HTTPS only:
GoogleAuthenticatorRails.cookie_options = { :httponly => true, :secure => true, :domain => :all }

Additional cookie option symbols can be found in the Ruby on Rails guide.

Destroying the Cookie

If you want to manually destroy the MFA cookie (for example, when a user logs out), just call

UserMfaSession::destroy

Storing Secrets in Encrypted Form

Normally, if an attacker gets access to the application database, they will be able to generate correct authentication codes, elmininating the security gains from two-factor authentication. If the application's secret_key_base is handled more securely than the database (by, for example, never putting it on the server filesystem), protection against database compromise can be gained by setting the :encrypt_secrets option to true. Newly-created secrets will then be stored in encrypted form.

Existing non-encrypted secrets for all models for which the :encrypt_secrets option has been set to true can be encrypted by running

  rails google_authenticator:encrypt_secrets

This may be reversed by running

  rails google_authenticator:decrypt_secrets

then by removing, or setting false, the :encrypt_secrets option.

If secret_key_base needs to change, set old_secret_key_base to the old key in config/secrets.yml before generating the new key. Then run

  rails google_authenticator:reencrypt_secrets

to change all encrypted google secret fields to use the new key.

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

License

MIT.