how to obtain proper 'call back URL'
You are getting 404 error because actually there is no page in your site with that url.

In your referenced tutorial the following statements can found as a note:

"
Note: The sample callback URL above is incorrectly shown. The callback URL should be an URL on the client side. When Drupal has authorized the consumer, it will call this URL with the access token as a parameter."

So you have to define a page call back with path as you want. You can define in your custom module.  OR You can give a valid site path as callback url. So When Drupal has authorized the consumer, it will call this URL with the access token as a parameter.