Add explicit handling for redirects

Motivation / Goals

Drupal redirects should work, not break the site by redirecting an API request to the frontend (thus serving html instead of the api request)

Example:* Redirect module is used to redirect /foo to /bar* Outcome: When I open a link /foo I'll endup on page /bar. Regardless of whether I use client side or server side navigation.

Currently the /foo request would be redirected to /bar - that shows the right content, but the site-visitors is not redirect to /bar. Insteads of redirecting the API request, the frontend must understand that the CMS wants to issue a redirect and follow that.

Solution

We introduce a new API key for sending "redirects" from the backend to the frontend in the lupus_ce_renderer response. When the new key "redirect" is set, all other keys may be omitted.

Backend code should be re-usable and go into the lupus_ce_renderer module, i.e. work with any module provide redirects - not just redirect module.

Frontend code should be re-usable and go into the nuxt drupal-ce module, so we can open a fitting PR there.

API data structure for redirects

# Redirect to Drupal-internal path

{ redirect: {
    external: false, 
    statusCode: 301,
    url: /some-path?with-query=1 
  } 
  # title, content, ... - can all be empty
} 

# Redirect to external URL  
{ 
  redirect: {
     external: true, 
    statusCode: 302,
     url: https://www.google.com }
}
  

Original report.

Problem/Motivation

Currently, redirects are not handled in a special way in lupus_ce_renderer. That's fine for Drupal internal redirects, but creates troubles when Drupal tries to issue an off-site redirect.

The goal of an off-site redirect is to redirect the browser to the this page, not the api client. Since the API client won't get custom-elements returned, this will lead to errors if not handled specifically.

However, it's not possible to handle this in the client during client side navigation, e.g. see https://github.com/axios/axios/issues/932#issuecomment-307390761

Proposed resolution

Add explicit redirect support: When rendering into custom elements, detect off-site redirects and render them in a special way which clients may interpret.

We can simply do this by adding a 'redirect' key to the page response json object instead of content.
On the client, e.g. for Nuxt we can then use e.g. the nuxt-redirect after fetching the response