Given a Dockerfile.template having:
```
FROM {{ registry }}/wikimedia-stretch
```
The Dockerfile has:
```
FROM docker-registry.discovery.wmnet/wikimedia-stretch
```
However trying to pull it yields:
```
$ docker pull docker-registry.discovery.wmnet/wikimedia-stretch
Using default tag: latest
Error response from daemon: Get https://docker-registry.discovery.wmnet/v2/wikimedia-stretch/manifests/latest: no basic auth credentials
```
But it works via the public endpoint:
```
$ docker pull docker-registry.wikimedia.org/wikimedia-stretch:latest
latest: Pulling from wikimedia-stretch
dea2308223aa: Already exists
Digest: sha256:e4da20099693c34ff780ed0766880e74ce3f479699bac51f212d57879b785a5b
Status: Downloaded newer image for docker-registry.wikimedia.org/wikimedia-stretch:latest
```
--------
From docker-pkg output:
```
2017-12-20 09:43:01,136 [docker-pkg-build] DEBUG - Looking for auth config (build.py:263)
2017-12-20 09:43:01,136 [docker-pkg-build] DEBUG - No auth config in memory - loading from filesystem (build.py:268)
2017-12-20 09:43:01,136 [docker-pkg-build] DEBUG - Trying paths: ['/home/hashar/.docker/config.json', '/home/hashar/.dockercfg'] (auth.py:234)
2017-12-20 09:43:01,136 [docker-pkg-build] DEBUG - No config file found (auth.py:241)
2017-12-20 09:43:01,136 [docker-pkg-build] DEBUG - No auth config found (build.py:308)
2017-12-20 09:43:01,221 [docker-pkg-build] DEBUG - http://localhost:None "POST /v1.30/build?pull=False&forcerm=False&rm=True&nocache=True&q=False&t=docker-registry.discovery.wmnet%2Freleng%2Fcastor%3A0.1.1...
2017-12-20 09:43:01,230 [docker-pkg-build] ERROR - Building image docker-registry.discovery.wmnet/releng/castor:0.1.1 failed - check your Dockerfile: Get https://docker-registry.discovery.wmnet/v2/wikimedia-stretch/manifests/latest: no basic auth credentials (image.py:228)
...
docker.errors.BuildError: Get https://docker-registry.discovery.wmnet/v2/wikimedia-stretch/manifests/latest: no basic auth credentials
```