DCI implementation of OAuth with Github in Sinatra

_app.rb

require "sinatra"

get "/oauth/github" do
  OAuthingWithGithub.start(self)
end

get "/oauth/github/callback" do
  OAuthingWithGithub.finish(self)
end

_oauthing_with_github.rb

# in contexts/oauthing_with_github.rb

class OAuthingWithGithub < AppContext
  def self.start(app)
    new(app).start
  end

  def self.finish(app)
    new(app).finish
  end

  def start
    unless session[:github_access_token]
      redirect OAuth::Github.authorize_url(config["github_key"],
                                           config["github_secret"], nil)

    end

    redirect "/"
  end

  def finish
    token = OAuth::Github.token(config["github_key"],
                                config["github_secret"],
                                params[:code])

    session[:github_access_token] = token

    user = User.new
    user.extend(Roles::GitHubber)
    user.find_or_create_from_github(token)

    redirect "/"
  end

  def config
    app.send(:env_from_config)
  end
  private :config

  module Roles
    module GitHubber
      def find_or_create_from_github(token)
        user = User.first_or_initialize(email: fetch_email(token))
        user.github_access_token = token
        user.save!
      end

      private

      def fetch_email(token)
        OAuth::Github::Client.get_email(token)
      end
    end
  end
end

app_context.rb

# in contexts/app_context.rb

class AppContext
  attr_reader :app

  def initialize(app)
    @app = app
  end

  private 

    def session
      app.session
    end

    def params
      app.params
    end

    def current_user
      app.current_user
    end

    def redirect(*attrs)
      app.redirect(*attrs)
    end
end

oauth.rb

# in oauth.rb
#
# a wrapper for OAuth client

require "oauth2"
require "httparty"
require "json"

module OAuth
  module Github
    def self.github_client(client_id, client_secret)
      OAuth2::Client.new(client_id, client_secret,
                         :authorize_url => 'https://github.com/login/oauth/authorize',
                         :token_url => 'https://github.com/login/oauth/access_token')
    end

    def self.authorize_url(client_id, client_secret, scope = "repo,gist")
      self.github_client(client_id, client_secret).auth_code.authorize_url(:scope => scope)
    end

    def self.token(client_id, client_secret, code)
      self.github_client(client_id, client_secret).auth_code.get_token(code).token
    end

    module Client
      def self.get_email(token)
        response = HTTParty.get("https://api.github.com/user", :query => {:access_token => token})
        body = JSON.parse(response.body)
        body["email"]
      end
    end
  end
end