Add Debian installation docs

doc/api/packages/debian.md

@@ -74,6 +74,38 @@ curl --request PUT \
      "https://gitlab.example.com/api/v4/projects/1/packages/debian/mypkg.deb"
 ```
 
+## Download a package
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64923) in GitLab 14.2.
+
+Download a package file.
+
+```plaintext
+GET projects/:id/packages/debian/pool/:distribution/:letter/:package_name/:package_version/:file_name
+```
+
+| Attribute         | Type   | Required | Description |
+| ----------------- | ------ | -------- | ----------- |
+| `distribution`    | string | yes      | The codename or suite of the Debian distribution. |
+| `letter`          | string | yes      | The Debian Classification (first-letter or lib-first-letter). |
+| `package_name`    | string | yes      | The source package name. |
+| `package_version` | string | yes      | The source package version. |
+| `file_name`       | string | yes      | The file name. |
+
+```shell
+curl --header "Private-Token: <personal_access_token>" "https://gitlab.example.com/api/v4/projects/1/packages/pool/my-distro/a/my-pkg/1.0.0/example_1.0.0~alpha2_amd64.deb"
+```
+
+Write the output to a file:
+
+```shell
+curl --header "Private-Token: <personal_access_token>" \
+     "https://gitlab.example.com/api/v4/projects/1/packages/pool/my-distro/a/my-pkg/1.0.0/example_1.0.0~alpha2_amd64.deb" \
+     --remote-name
+```
+
+This writes the downloaded file using the remote file name in the current directory.
+
 ## Route prefix
 
 The remaining endpoints described are two sets of identical routes that each make requests in
@@ -108,7 +140,7 @@ The examples in this document all use the project-level prefix.
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64067) in GitLab 14.1.
 
-Download a Debian package file.
+Download a Debian distribution file.
 
 ```plaintext
 GET <route-prefix>/dists/*distribution/Release
@@ -130,16 +162,13 @@ curl --header "Private-Token: <personal_access_token>" \
      --remote-name
 ```
 
-This writes the downloaded file to `Release` in the current directory.
+This writes the downloaded file using the remote file name in the current directory.
 
 ## Download a signed distribution Release file
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64067) in GitLab 14.1.
 
-Download a Debian package file.
-
-Signed releases are [not supported](https://gitlab.com/groups/gitlab-org/-/epics/6057#note_582697034).
-Therefore, this endpoint downloads the unsigned release file.
+Download a signed Debian distribution file.
 
 ```plaintext
 GET <route-prefix>/dists/*distribution/InRelease
@@ -161,4 +190,62 @@ curl --header "Private-Token: <personal_access_token>" \
      --remote-name
 ```
 
-This writes the downloaded file to `InRelease` in the current directory.
+This writes the downloaded file using the remote file name in the current directory.
+
+## Download a release file signature
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64923) in GitLab 14.2.
+
+Download a Debian release file signature.
+
+```plaintext
+GET <route-prefix>/dists/*distribution/Release.gpg
+```
+
+| Attribute         | Type   | Required | Description |
+| ----------------- | ------ | -------- | ----------- |
+| `distribution`    | string | yes      | The codename or suite of the Debian distribution. |
+
+```shell
+curl --header "Private-Token: <personal_access_token>" "https://gitlab.example.com/api/v4/projects/1/packages/debian/dists/my-distro/Release.gpg"
+```
+
+Write the output to a file:
+
+```shell
+curl --header "Private-Token: <personal_access_token>" \
+     "https://gitlab.example.com/api/v4/projects/1/packages/debian/dists/my-distro/Release.gpg" \
+     --remote-name
+```
+
+This writes the downloaded file using the remote file name in the current directory.
+
+## Download a binary file's index
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64923) in GitLab 14.2.
+
+Download a distribution index.
+
+```plaintext
+GET <route-prefix>/dists/*distribution/:component/binary-:architecture/Packages
+```
+
+| Attribute         | Type   | Required | Description |
+| ----------------- | ------ | -------- | ----------- |
+| `distribution`    | string | yes      | The codename or suite of the Debian distribution. |
+| `component`       | string | yes      | The distribution component name. |
+| `architecture`    | string | yes      | The distribution architecture type. |
+
+```shell
+curl --header "Private-Token: <personal_access_token>" "https://gitlab.example.com/api/v4/projects/1/packages/debian/dists/my-distro/main/amd64/Packages"
+```
+
+Write the output to a file:
+
+```shell
+curl --header "Private-Token: <personal_access_token>" \
+     "https://gitlab.example.com/api/v4/projects/1/packages/debian/dists/my-distro/main/amd64/Packages" \
+     --remote-name
+```
+
+This writes the downloaded file using the remote file name in the current directory.

doc/user/packages/debian_repository/index.md

@@ -61,6 +61,15 @@ Feature.disable(:debian_group_packages)
 
 Creating a Debian package is documented [on the Debian Wiki](https://wiki.debian.org/Packaging).
 
+## Authenticate to the Package Registry
+
+To create a distribution, publish a package, or install a private package, you need one of the
+following:
+
+- [Personal access token](../../../api/index.md#personalproject-access-tokens)
+- [CI/CD job token](../../../api/index.md#gitlab-cicd-job-token)
+- [Deploy token](../../project/deploy_tokens/index.md)
+
 ## Create a Distribution
 
 On the project-level, Debian packages are published using *Debian Distributions*. To publish
@@ -116,7 +125,7 @@ To upload these files, you can use `dput-ng >= 1.32` (Debian bullseye):
 cat <<EOF > dput.cf
 [gitlab]
 method = https
-fqdn = <login>:<your_access_token>@gitlab.example.com
+fqdn = <username>:<your_access_token>@gitlab.example.com
 incoming = /api/v4/projects/<project_id>/packages/debian
 EOF
 
@@ -125,5 +134,27 @@ dput --config=dput.cf --unchecked --no-upload-log gitlab <your_package>.changes
 
 ## Install a package
 
-The Debian package registry for GitLab is under development, and isn't ready for production use. You
-cannot install packages from the registry. However, you can download files directly from the UI.
+To install a package:
+
+1. Configure the repository:
+
+    If you are using a private project, add your [credentials](#authenticate-to-the-package-registry) to your apt config:
+
+    ```shell
+    echo 'machine gitlab.example.com login <username> password <your_access_token>' \
+      | sudo tee /etc/apt/auth.conf.d/gitlab_project.conf
+    ```
+
+    Add your project as a source:
+
+    ```shell
+    echo 'deb [trusted=yes] https://gitlab.example.com/api/v4/projects/<project_id>/packages/debian <codename> <component1> <component2>' \
+      | sudo tee /etc/apt/sources.list.d/gitlab_project.list
+    sudo apt-get update
+    ```
+
+1. Install the package:
+
+    ```shell
+    sudo apt-get -y install -t <codename> <package-name>
+    ```