title: Unable to use devise_token_auth with active_admin
body: <p>I'm trying to used devise_token_auth with active_admin. When running <code>rails g active_admin:install User</code> I get the following error.</p>
  
  <h3>error</h3>
  
  <blockquote>
    <p>usr/local/lib/ruby/gems/2.4.0/gems/actionpack-5.1.4/lib/action_dispatch/routing/route_set.rb:578:in
    <code>add_route': Invalid route name, already in use: 'new_user_session' 
    You may have defined two routes with the same name using the</code>:as`
    option, or you may be overriding a route already defined by a resource
    with the same naming.</p>
  </blockquote>
  
  <h3>routes.rb</h3>
  
  <pre><code>Rails.application.routes.draw do
    devise_for :users, ActiveAdmin::Devise.config
    ActiveAdmin.routes(self)
    mount_devise_token_auth_for 'User', at: 'auth'
  
    scope module: 'api' do
      namespace :v1 do
        resources :users, only: [:index, :show]
      end
    end
  
    get '/docs' =&gt; redirect('/swagger/dist/index.html?url=/apidocs/api-docs.json')
  end
  </code></pre>