Unable to Download Go Modules from Private GitLab Repository in Docker Container Using Docker Compose on Windows

Question

I have two private GitLab repositories: webserver and helper, both written in Golang.

The webserver/main.go is as simple as this:

package main

import (
    "net/http"

    "github.com/labstack/echo/v4"
    "gitlab.com/randomname/helper"
)

func main() {
    e := echo.New()

    e.GET("/greet", func(c echo.Context) error {
        greet := helper.Greetings()
        return c.String(http.StatusOK, greet)
    })

    e.Logger.Fatal(e.Start(":1323"))
}

The helper repository contains a single file: helper/helper.go

package helper

func Greetings() string {
    return "Halo, how are you?"
}

I can run this locally without any issues using the replace directive in the go.mod file. I’ve also successfully set up SSH keys on my GitLab account for pulling and pushing the repositories.

Problem

When I try to run this service locally using Docker, I encounter issues. Below is the Dockerfile I use in the webserver repository:

FROM golang:1.23-alpine AS builder

ENV GOPRIVATE="gitlab.com/randomname/*" GO111MODULE=on CGO_ENABLED=0 GOOS=linux GOARCH=amd64

RUN apk --no-cache add ca-certificates git openssh

RUN mkdir /root/.ssh/
RUN echo "${SSH_PRIVATEKEY}" > /root/.ssh/id_rsa
RUN chmod 600 /root/.ssh/id_rsa
RUN touch /root/.ssh/known_hosts
RUN ssh-keyscan gitlab.com >> /root/.ssh/id_rsa

RUN git config --global url.git@gitlab.com:.insteadOf https://gitlab.com/

WORKDIR /build 

COPY go.mod .
COPY go.sum .

RUN go mod download

COPY . .

RUN go build -o webserver

FROM alpine:3.12

WORKDIR /app

COPY --from=builder /build/webserver /app/

cmd ["./webserver"]

I run the service using the following docker-compose.yml file:

services:
  webserver:
    build:
      context: ../webserver
      dockerfile: Dockerfile
      args:
        SSH_PRIVATEKEY: ${SSH_PRIVATEKEY}
    ports: 
    - "8000:1323"

The error when I run docker compose up --build is like

 => ERROR [webserver builder 12/14] RUN go mod download 

1.561   Host key verification failed.
1.561   fatal: Could not read from remote repository.
1.561 
1.561   Please make sure you have the correct access rights
1.561   and the repository exists.

I have similar setup on MacOS and it works fine. However, when I try running it on Windows I got the problem. I already tried both via WSL and the Windows itself and the result still same.

Does anyone have suggestions for troubleshooting this issue or making it work on Windows?