Allows otp_length to be configurable

Adds otp_length to options in README

Sets default length to 6

README.md

@@ -38,11 +38,12 @@ Add the following line to your model to fully enable two-factor auth:
 
     has_one_time_password
 
-Set config values if desired for maximum second factor attempts count and allowed time drift for one-time passwords:
+Set config values, if desired, for maximum second factor attempts count, allowed time drift, and OTP length.
 
 ```ruby
 config.max_login_attempts = 3
 config.allowed_otp_drift_seconds = 30
+config.otp_length = 6
 ```
 
 Override the method to send one-time passwords in your model, this is automatically called when a user logs in:
@@ -66,11 +67,12 @@ Add the following line to your model to fully enable two-factor auth:
 
     has_one_time_password
 
-Set config values if desired for maximum second factor attempts count and allowed time drift for one-time passwords:
+Set config values, if desired, for maximum second factor attempts count, allowed time drift, and OTP length.
 
 ```ruby
 config.max_login_attempts = 3
 config.allowed_otp_drift_seconds = 30
+config.otp_length = 6
 ```
 
 Override the method to send one-time passwords in your model, this is automatically called when a user logs in:
@@ -81,6 +83,7 @@ def send_two_factor_authentication_code
 end
 ```
 
+
 ### Customisation and Usage
 
 By default second factor authentication enabled for each user, you can change it with this method in your User model:

lib/two_factor_authentication.rb

@@ -13,6 +13,9 @@ module Devise
 
   mattr_accessor :allowed_otp_drift_seconds
   @@allowed_otp_drift_seconds = 30
+
+  mattr_accessor :otp_length
+  @@otp_length = 6
 end
 
 module TwoFactorAuthentication

lib/two_factor_authentication/models/two_factor_authenticatable.rb

@@ -20,19 +20,19 @@ module Devise
             end
           end
         end
-        ::Devise::Models.config(self, :max_login_attempts, :allowed_otp_drift_seconds)
+        ::Devise::Models.config(self, :max_login_attempts, :allowed_otp_drift_seconds, :otp_length)
       end
 
       module InstanceMethodsOnActivation
         def authenticate_otp(code, options = {})
-          totp = ROTP::TOTP.new(self.otp_column)
+          totp = ROTP::TOTP.new(self.otp_column, { digits: options[:otp_length] || self.class.otp_length })
           drift = options[:drift] || self.class.allowed_otp_drift_seconds
 
           totp.verify_with_drift(code, drift)
         end
 
-        def otp_code(time = Time.now)
+        def otp_code(time = Time.now, options = {})
-          ROTP::TOTP.new(self.otp_column).at(time, true)
+          ROTP::TOTP.new(self.otp_column, { digits: options[:otp_length] || self.class.otp_length }).at(time, true)
         end
 
         def provisioning_uri(account = nil, options = {})

spec/lib/two_factor_authentication/models/two_factor_authenticatable_spec.rb

@@ -21,11 +21,15 @@ describe Devise::Models::TwoFactorAuthenticatable, '#otp_code' do
       subject
     end
 
+    it "should be configured length" do
+      expect(subject.length).to eq(Devise.otp_length)
+    end
+
     context "with a known time" do
       let(:time) { 1392852756 }
 
       it "should return a known result" do
-        expect(subject).to eq('562202')
+        expect(subject).to eq("0000000524562202".split(//).last(Devise.otp_length).join)
       end
     end
 
@@ -33,7 +37,7 @@ describe Devise::Models::TwoFactorAuthenticatable, '#otp_code' do
       let(:time) { 1393065856 }
 
       it "should return a known result padded with zeroes" do
-        expect(subject).to eq('007672')
+        expect(subject).to eq("0000001608007672".split(//).last(Devise.otp_length).join)
       end
     end
   end

spec/support/features_spec_helper.rb

@@ -8,7 +8,7 @@ module FeaturesSpecHelper
   def complete_sign_in_form_for(user)
     fill_in "Email", with: user.email
     fill_in "Password", with: 'password'
-    click_button "Sign in"
+    click_button "Log in"
   end
 end