build.sh

$ docker build --ssh default .
$ docker build --secret id=netrc,src=netrc --build-arg CI=1 .

Dockerfile

FROM golang:latest

WORKDIR /build
COPY . .

ARG GITHUB_HOST_KEY_ED25519="AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl"

ARG CI
ARG GIT_CONFIG_COUNT=${CI:+0}

ENV GIT_CONFIG_COUNT ${GIT_CONFIG_COUNT:-1}
ENV GIT_CONFIG_KEY_0 "url.ssh://git@github.com.insteadOf"
ENV GIT_CONFIG_VALUE_0 "https://github.com"

RUN mkdir ~/.ssh
COPY <<-EOF /root/.ssh/known_hosts
    github.com ssh-ed25519 ${GITHUB_HOST_KEY_ED25519}
EOF

RUN --mount=type=secret,id=netrc,dst=/root/.netrc \
    --mount=type=ssh \
        go mod tidy

netrc

machine github.com
password ${PAT}
login oauth2