Serve external version through El Proxito

[humitos]

Allow El Proxito to serve EXTERNAL versions.

Before this PR, we were serving external version just by using an NGINX proxy_pass rule pointing to the Blob storage. This new behavior is cleaner but also required to serve these versions on corporate, since they require auth and El Proxito can handle it properly.

Steps to test this PR

Import readthedocs/test-builds into your local instance:

python manage.py import_project_from_live test-builds

Then, open a Django shell and create an external version pointing to PR 13 in that repository:

project = Project.objects.get(slug='test-builds')
version = Version.objects.create(project=project, type='external', active=True, verbose_name='13', slug='13', identifier='617672ce68a24c4397ae009a69b4d93850e4b8b6')

You can also setup a OAuth GitHub application, connect your GH account, etc but that's too complicated just for testing accessing to an external version documentation.

Finally, trigger a build for that version:

from readthedocs.core.utils import trigger_build
trigger_build(project, version)

At this point, you will be able to hit http://external-builds.community.dev.readthedocs.io/html/test-builds/13/index.html and see the documentation built from a PR properly.

[ericholscher]

This feels way cleaner than our previous approach. I really like it.

This is also blocked on shipping proxito, sadly. I think we could start routing /_/ from our docs domains to proxito if we wanted, that would let us ship this and the media downloads.

Also, the URL that it links to now is http://test-builds.community.dev.readthedocs.io/_/external/html/test-builds/13/index.html for me locally 👍

[humitos]

Originally, this PR was serving PR builds at a different domain than the docs domain:

At this point, you will be able to hit http://external-builds.community.dev.readthedocs.io/html/test-builds/13/index.html and see the documentation built from a PR properly.

Then we decided that it could be good to serve it under the same domain as the docs:

Also, the URL that it links to now is http://test-builds.community.dev.readthedocs.io/_/external/html/test-builds/13/index.html for me locally +1

Although, we realize that this is a potential security issue on projects with custom domains.

[ericholscher]

This looks mergable to me now 👍

We'll need to also change the nginx configs in prod to support this, but that's good since we can easily deploy and test this.

[humitos]

We'll need to also change the nginx configs in prod to support this, but that's good since we can easily deploy and test this.

If I understand correctly, we can safely deploy these changes and they won't have any effect in production until we change the NGINX config file to start using El Proxito. In fact, after deploying this, it should be working in our test-builds project which has El Proxito enabled.

So, I think we are good to merge this and safely deploy in the next deploy.