Merge branch 'docs/add-proxying-assets-content-from-omnibus' into 'master'

Combine asset proxying content from Omnibus

See merge request gitlab-org/gitlab-ce!32807

doc/security/asset_proxy.md

+# Proxying assets
+
 A possible security concern when managing a public facing GitLab instance is
 the ability to steal a users IP address by referencing images in issues, comments, etc.
 
 For example, adding `![Example image](http://example.com/example.png)` to
 an issue description will cause the image to be loaded from the external
-server in order to be displayed.  However this also allows the external server
+server in order to be displayed. However, this also allows the external server
 to log the IP address of the user.
 
 One way to mitigate this is by proxying any external images to a server you
-control.  GitLab handles this by allowing you to run the "Camo" server
-[cactus/go-camo](https://github.com/cactus/go-camo#how-it-works).
-The image request is sent to the Camo server, which then makes the request for
-the original image.  This way an attacker only ever seems the IP address
-of your Camo server.
+control.
+
+GitLab can be configured to use an asset proxy server when requesting external images/videos in
+issues, comments, etc. This helps ensure that malicious images do not expose the user's IP address
+when they are fetched.
+
+We currently recommend using [cactus/go-camo](https://github.com/cactus/go-camo#how-it-works)
+as it supports proxying video and is more configurable.
+
+## Installing Camo server
+
+A Camo server is used to act as the proxy.
+
+To install a Camo server as an asset proxy:
+
+1. Deploy a `go-camo` server. Helpful instructions can be found in
+   [building catus/go-camo](https://github.com/cactus/go-camo#building).
+
+1. Make sure your instance of GitLab is running, and that you have created a private API token.
+   Using the API, configure the asset proxy settings on your GitLab instance. For example:
+
+    ```sh
+    curl --request "PUT" "https://gitlab.example.com/api/v4/application/settings?\
+    asset_proxy_enabled=true&\
+    asset_proxy_url=https://proxy.gitlab.example.com&\
+    asset_proxy_secret_key=<somekey>" \
+    --header 'PRIVATE-TOKEN: <my_private_token>'
+    ```
+
+    The following settings are supported:
+
+    | Attribute                | Description                                                                                                                          |
+    |:-------------------------|:-------------------------------------------------------------------------------------------------------------------------------------|
+    | `asset_proxy_enabled`    | Enable proxying of assets. If enabled, requires: `asset_proxy_url`).                                                                 |
+    | `asset_proxy_secret_key` | Shared secret with the asset proxy server.                                                                                           |
+    | `asset_proxy_url`        | URL of the asset proxy server.                                                                                                       |
+    | `asset_proxy_whitelist`  | Assets that match these domain(s) will NOT be proxied. Wildcards allowed. Your GitLab installation URL is automatically whitelisted. |
+
+1. Restart the server for the changes to take effect. Each time you change any values for the asset
+   proxy, you need to restart the server.
+
+## Using the Camo server
+
+Once the Camo server is running and you've enabled the GitLab settings, any image or video that
+references an external source will get proxied to the Camo server.
 
-Once you have your Camo server up and running, you can configure GitLab to
-proxy image requests to it.  The following settings are supported:
+For example, the following is a link to an image in Markdown:
 
-| Attribute                 | Description |
-| ------------------------- | ----------- |
-| `asset_proxy_enabled`     | (**If enabled, requires:** `asset_proxy_url`) Enable proxying of assets. |
-| `asset_proxy_secret_key`  | Shared secret with the asset proxy server. |
-| `asset_proxy_url`         | URL of the asset proxy server. |
-| `asset_proxy_whitelist`   | Assets that match these domain(s) will NOT be proxied. Wildcards allowed. Your GitLab installation URL is automatically whitelisted. |
+```markdown
+![logo](https://about.gitlab.com/images/press/logo/jpg/gitlab-icon-rgb.jpg)
+```
 
-These can be set via the [Application setting API](../api/settings.md)
+The following is an example of a source link that could result:
 
-Note that a GitLab restart is required to apply any changes.
+```text
+http://proxy.gitlab.example.com/f9dd2b40157757eb82afeedbf1290ffb67a3aeeb/68747470733a2f2f61626f75742e6769746c61622e636f6d2f696d616765732f70726573732f6c6f676f2f6a70672f6769746c61622d69636f6e2d7267622e6a7067
+```