Make the dependency proxy host configurable

🍎 Proposal

The first step in implementing generic image registry support for dependency proxy is removing the hardcoded sections of dependency proxy code.

Task 1: Make the dependency proxy more dynamic

  1. Add an application settings to hold the default host for the dependency proxy:

    container_dependency_proxy_default_host = 'https://registry-1.docker.io'

    This setting should be accessible via the API and the admin UI. It should require admin permissions to update.

  2. Update the DependencyProxy::Registry model and the DependencyProxy::RequestTokenService.

    The RequestTokenService should make an additional request before it gets the auth_url. First it needs to make an empty curl request to the default host with a path of /v2/. The response will be a 401 unauthorized and the www-authenticate header should be parsed to obtain the Bearer realm value, and the service value:

    curl -i https://registry-1.docker.io/v2/
HTTP/1.1 401 Unauthorized
content-type: application/json
docker-distribution-api-version: registry/2.0
www-authenticate: Bearer realm="https://auth.docker.io/token",service="registry.docker.io"
date: Mon, 24 May 2021 17:42:06 GMT
content-length: 87
strict-transport-security: max-age=31536000

{"errors":[{"code":"UNAUTHORIZED","message":"authentication required","detail":null}]}

    You can now see how those values should be used to build the auth_url in the DependencyProxy::Registry model.

    The goal is to remove the AUTH_URL and LIBRARY_URL constants, and update the various methods using those values to instead use the new application setting value along with the values returned in the initial request header when needed.

📄 Related issues and epics

Edited by 🤖 GitLab Bot 🤖