en_oauth.rb

get '/callback' do
  unless params['oauth_verifier'] || session['request_token']
    @last_error = "Content owner did not authorize the temporary credentials"
    halt erb :error
  end
  session[:oauth_verifier] = params['oauth_verifier']
  begin
    session[:access_token] = session[:request_token].get_access_token(:oauth_verifier => session[:oauth_verifier])
    redirect '/list'
  rescue => e
    @last_error = 'Error extracting access token'
    erb :error
  end
end