After a 401 the transport fetches a token from the challenge's realm,
using credentials configured for that realm, and sends it to the host
that issued the challenge. It trusted that host if it had any configured
credentials, even unrelated ones, or shared the realm's registrable
domain. The second rule makes every tenant on a shared domain such as
jfrog.io, azurecr.io or pkg.dev the same site, and the first hands a
token minted from one registry's credentials to another registry the
proxy happens to have a key for.
A credentialed token now goes only to a registry on the realm's own
host and port, to one configured with the same credentials as the
realm, or to Docker Hub and GitLab.com, whose registries use a token
service on another host. Anonymous tokens are unaffected.
The scope in the token request also came from the challenge, so a
registry could ask for push access or for other repositories. The proxy
only reads, so it now always asks for pull access to the repository in
the request path.
Credentials configured for a token service were applied to any challenge
naming it. A host the proxy fetches from, such as one in a Composer dist
URL or a Helm index, could answer a /v2/ request with a Bearer challenge
naming that realm, and the proxy fetched a token with the configured
credentials and sent it to that host. A token cached from a legitimate
pull was handed over the same way.
- Follow a challenge to a realm with configured credentials only for a
registry that has configured credentials of its own, or is on the same
site (registrable domain) as the realm, as registry-1.docker.io is with
auth.docker.io; otherwise pass the 401 back
- Keep following anonymous challenges for any registry, as before
- Document the rule
