How can a controller respond with an action to redirect from another website in Ruby

Question

I am a newbie in ruby. I want to post a form data which includes an API key and some other field data to another website which will verify and send an http response 200 or 400 to my website. If I am able to connect to the api, the website responds with a URL redirect to my website with additional query string which my website will respond to. I don't how to do the following:

How to make my site respond to the redirect I get from the website through a controller and action. Assuming the controller is:

 class BooksController < ApplicationController

  def create
   Do something

   flash[:notice] = " book was created successfully"
  end

end

Configure my route to respond to the redirect

here is the code I am trying to use on view

   <form action="/master/master" method="POST" >
    <script
    src="https://js.example.co/v7/inline.js" 
    data-key= <%= ENV["EXAMPLE_PUBLIC_KEY"] %>
    data-email= <%= current_user.email %> 
    data-booktitle= <%= current_user.books.title %>
    data-ref= <% SecureRandom.random_number %> 
 >
  </script> 
  </form>

Answer 1

This is just the basics of how to post a form to an external website. You'll have to fill in the details yourself since I have no clue what the external website does or what that script is supposed to accomplish.

Setting up a form to post to a remote url is pretty easy:

# Rails 4 and earlier
<% form_tag("http://example.com/test.php", method: :post) %>
  <%= hidden_field_tag :key, ENV["EXAMPLE_PUBLIC_KEY"] %>
  <%= hidden_field_tag :title, current_user.books.title %>
  <%= hidden_field_tag :ref, SecureRandom.random_number %>
  <%= submit_tag %>
<% end %>

# Rails 5+
<%= form_with(url: "http://example.com/test.php", method: :post) do |f| %>
  <%= f.hidden_field :key, value: ENV["EXAMPLE_PUBLIC_KEY"] %>
  # ...
<% end %>

Handling the callback from the external website isn't really different then any other route in your rails app:

get '/some/path', to: 'foo#bar'

You just create a route that responds to GET, and configure whatever service that handles the form submission to redirect back to it.