Support GitLab dependency proxy when building gitlab-tofu images

Closes https://gitlab.com/components/opentofu/-/issues/70

Changelog: feature

.gitlab-ci.yml

@@ -89,6 +89,20 @@ gitlab-opentofu-image:build:
   stage: build
   image: quay.io/containers/buildah:v1.37.3
   before_script:
+    # Supporting GitLab dependency proxies:
+    # see https://docs.gitlab.com/ee/user/packages/dependency_proxy/
+    - |
+      if [ -n "$CI_DEPENDENCY_PROXY_DIRECT_GROUP_IMAGE_PREFIX" ]; then
+        echo "Detected GitLab Dependency Proxy at '$CI_DEPENDENCY_PROXY_DIRECT_GROUP_IMAGE_PREFIX', configuring it for buildah ..."
+        cat > /etc/containers/registries.conf.d/dependency-proxy.conf <<EOF
+        [[registry]]
+        location = "docker.io"
+        [[registry.mirror]]
+        location = "${CI_DEPENDENCY_PROXY_DIRECT_GROUP_IMAGE_PREFIX}"
+      EOF
+
+        buildah login -u "$CI_DEPENDENCY_PROXY_USER" -p "$CI_DEPENDENCY_PROXY_PASSWORD" "$CI_DEPENDENCY_PROXY_SERVER"
+      fi
     - buildah login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" "$CI_REGISTRY"
   script:
     - echo "Building $GITLAB_OPENTOFU_IMAGE_NAME"

.gitlab/README.md.template

@@ -396,6 +396,11 @@ See also the official GitLab documentation for it
 If you want to save runner resources you may disable the unit and integration tests
 by setting the `SKIP_TESTS` CI/CD variable to `true`.
 
+The pipeline of this component respects the
+[GitLab Dependency Proxy](https://docs.gitlab.com/ee/user/packages/dependency_proxy/) configuration
+by detecting the `CI_DEPENDENCY_PROXY_DIRECT_GROUP_IMAGE_PREFIX` environment variable
+and configuring `buildah` to use it when building the container images.
+
 ## Migrating from the Terraform CI/CD templates
 
 When migrating from the GitLab Terraform CI/CD templates you can use the following migration rules:

README.md

@@ -415,6 +415,11 @@ See also the official GitLab documentation for it
 If you want to save runner resources you may disable the unit and integration tests
 by setting the `SKIP_TESTS` CI/CD variable to `true`.
 
+The pipeline of this component respects the
+[GitLab Dependency Proxy](https://docs.gitlab.com/ee/user/packages/dependency_proxy/) configuration
+by detecting the `CI_DEPENDENCY_PROXY_DIRECT_GROUP_IMAGE_PREFIX` environment variable
+and configuring `buildah` to use it when building the container images.
+
 ## Migrating from the Terraform CI/CD templates
 
 When migrating from the GitLab Terraform CI/CD templates you can use the following migration rules: