Copy credentials into build container for git cloning, etc

go-builder.Dockerfile

FROM iron/go:dev as builder

ARG GH_TOKEN=default
RUN echo "machine github.com" > "/root/.netrc" \
  && \
    echo "login x-oath-basic" >> "/root/.netrc" \
  && \
    echo "password $GH_TOKEN" >> "/root/.netrc" \
  && \
    chmod 600 /root/.netrc
    
# Do go get; go build, etc

# create deployment image
FROM alpine

RUN apk add --no-cache ca-certificates

COPY --from=builder path/to/binary /bin/binary