Fix anonymous access for other registries

[tm-drtina]

This should allow anonymous access to other registries than Docker Hub by parsing WWW-Authenticate header instead of havin hardcoded URLs for hub.

The parser is done according to RFC7235
https://datatracker.ietf.org/doc/html/rfc7235#autoid-30

Closes #68

Manual testing done:

Verification of how different registries handle anonymous access:

Google Container/Artifact Registry

$ curl --dump-header - https://gcr.io/v2/distroless/nodejs/manifests/latest 
HTTP/2 200 
content-length: 741
content-type: application/vnd.docker.distribution.manifest.list.v2+json
docker-content-digest: sha256:b534f9b5528e69baa7e8caf7bcc1d93ecf59faa15d289221decf5889a2ed3877
docker-distribution-api-version: registry/2.0
x-gcr-using-artifact-registry: true
server: Docker Registry

{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [ ... ]
}

Docker Hub

$ curl --dump-header - https://registry-1.docker.io/v2/library/node/manifests/latest 
HTTP/2 401 
content-type: application/json
content-length: 155
docker-distribution-api-version: registry/2.0
www-authenticate: Bearer realm="https://auth.docker.io/token",service="registry.docker.io",scope="repository:library/node:pull"

{"errors":[{"code":"UNAUTHORIZED","message":"authentication required","detail":[{"Type":"repository","Class":"","Name":"library/node","Action":"pull"}]}]}

Running hocker-manifest

Google Container/Artifact Registry

$ cabal run hocker-manifest -- --registry https://gcr.io distroless/nodejs latest
{"schemaVersion":2,"mediaType":"application/vnd.docker.distribution.manifest.v2+json","config":{"mediaType":"application/vnd.docker.container.image.v1+json","size":967,"digest":"sha256:cf46b336f6597ef45686d6f517a12c43466b85fbdff5cff01ff7d8109db47046"},"layers":[...]}

Docker Hub

$ cabal run hocker-manifest -- library/node latest
{"manifests":[...],"mediaType":"application\/vnd.oci.image.index.v1+json","schemaVersion":2}

[jsoo1]

Thank you! This LGTM, but I would like some notes on testing done for this.

[tm-drtina]

I've added some unit tests for the parser. I was testing it with Docker Hub registry and our internal one (both headers added to test cases, though obfuscated). Also checked gcr.io, but they allow anonymous access without tokens

[jsoo1]

I've added some unit tests for the parser. I was testing it with Docker Hub registry and our internal one (both headers added to test cases, though obfuscated). Also checked gcr.io, but they allow anonymous access without tokens

If you wouldn't mind adding the manual tests done to the PR description, that would be excellent.

[jsoo1]

Thank you very much, no more blocking issues from me.

[jsoo1]

Reaffirming the approval. Thank you!