title: Rails app in subdirectory in production not redirecting properly to install shopify store
body: <p>Using localhost:3000 I was able to install the shopify store and interact with it. However, when deploying it into production, which is in a subdirectory (www.website.com/app_name), the "login" for the shop is redirected to root and not to the subdirectory. I whitelisted the redirect urls in the shopify app dashboard.</p>
  
  <p>In omniauth.rb</p>
  
  <pre><code>callback_url: "http://{domain}/{app_name}/auth/shopify/callback"
  </code></pre>
  
  <p>In routes.rb</p>
  
  <pre><code>mount ShopifyApp::Engine, at: '/{app_name}'
  </code></pre>
  
  <p>Apart from the code above, the settings for shopify are the ones that the generator created. Any ideas in how to fix this?</p>
  
  <p>Tanks!</p>