enable two-factor authentication

fixes #399

http://developer.github.com/v3/auth/#working-with-two-factor-authentication

features/authentication.feature

@@ -97,3 +97,32 @@ Feature: OAuth authentication
     Then the stderr should contain "Error creating repository: Unauthorized (HTTP 401)"
     And the exit status should be 1
     And the file "../home/.config/hub" should not exist
+
+  Scenario: Two-factor authentication
+    Given the GitHub API server:
+      """
+      require 'rack/auth/basic'
+      get('/authorizations') {
+        auth = Rack::Auth::Basic::Request.new(env)
+        halt 401 unless auth.credentials == %w[mislav kitty]
+        if request.env['HTTP_X_GITHUB_OTP'] != "112233"
+          response.headers['X-GitHub-OTP'] = "required;application"
+          halt 401
+        end
+        json [ {:token => 'OTOKEN', :app => {:url => 'http://hub.github.com/'}} ]
+      }
+      get('/user') {
+        json :login => 'mislav'
+      }
+      post('/user/repos') {
+        json :full_name => 'mislav/dotfiles'
+      }
+      """
+    When I run `hub create` interactively
+    When I type "mislav"
+    And I type "kitty"
+    And I type "112233"
+    Then the output should contain "github.com password for mislav (never stored):"
+    Then the output should contain "two-factor authentication code:"
+    And the exit status should be 0
+    And the file "../home/.config/hub" should contain "oauth_token: OTOKEN"

lib/hub/github_api.rb

@@ -257,10 +257,19 @@ def apply_authentication req, url
         end
       end
 
-      def obtain_oauth_token host, user
+      def obtain_oauth_token host, user, two_factor_code = nil
         # first try to fetch existing authorization
-        res = get "https://#{user}@#{host}/authorizations"
-        res.error! unless res.success?
+        res = get "https://#{user}@#{host}/authorizations" do |req|
+          req['X-GitHub-OTP'] = two_factor_code if two_factor_code
+        end
+        unless res.success?
+          if !two_factor_code && res['X-GitHub-OTP'].to_s.include?('required')
+            two_factor_code = config.prompt_auth_code
+            return obtain_oauth_token(host, user, two_factor_code)
+          else
+            res.error!
+          end
+        end
 
         if found = res.data.find {|auth| auth['app']['url'] == oauth_app_url }
           found['token']
@@ -401,6 +410,13 @@ def prompt_password host, user
         abort
       end
 
+      def prompt_auth_code
+        print "two-factor authentication code: "
+        $stdin.gets.chomp
+      rescue Interrupt
+        abort
+      end
+
       NULL = defined?(File::NULL) ? File::NULL :
                File.exist?('/dev/null') ? '/dev/null' : 'NUL'