Rerwite the "Additional preview environments support" article and correct URL provider references

17/umbraco-cms/reference/content-delivery-api/additional-preview-environments-support.md

@@ -5,21 +5,120 @@ description: >-
 
 # Additional preview environments support
 
-{% hint style="warning" %}
-The original contents of this article, explaining how to change the backoffice UI, does not apply anymore to Umbraco 15 and above and has been removed.
-The way to achieve this beyond Umbraco 14 is to create and register an [Extension](../../customizing/extending-overview) to modify the backoffice UI preview button.
-{% endhint %}
-
-With Umbraco, you can save and preview draft content before going live. The preview feature allows you to visualize how a page will look like once it is published, directly from within the backoffice. This is also possible for the Content Delivery API data. You can extend the preview functionality in the backoffice by configuring external preview URLs for client libraries consuming the Content Delivery API.
+With Umbraco, you can save and preview draft content before going live. The preview feature allows you to visualize how a page will look once it is published, directly from within the backoffice. This is also possible for the Content Delivery API data. You can extend the preview functionality in the backoffice by configuring external preview URLs for client libraries consuming the Content Delivery API.
 
 {% hint style="info" %}
-To get introduced to the preview functionality in the Content Delivery API, please refer to the [Preview concept](https://docs.umbraco.com/umbraco-cms/reference/content-delivery-api#preview) section.
+To learn more about the preview functionality in the Content Delivery API, see the [Preview concept](https://docs.umbraco.com/umbraco-cms/reference/content-delivery-api#preview) section.
 {% endhint %}
 
+Generating external preview URLs for the backoffice requires implementation on both the client and server sides.
+
+## Server-side implementation
+
+On the server-side, you'll need a custom `IUrlProvider` implementation. This is responsible for generating the preview URL for a given piece of content.
+
+An external preview environment likely requires some kind of authentication to allow preview. The URL provider should perform this as well.
+
+Here's an example of what a URL provider could look like:
+
+{% code title="MyUrlProvider.cs" lineNumbers="true" %}
+```csharp
+using Umbraco.Cms.Core.Models;
+using Umbraco.Cms.Core.Models.PublishedContent;
+using Umbraco.Cms.Core.Routing;
+
+namespace My.Site;
+
+public class MyUrlProvider : IUrlProvider
+{
+    public string Alias => "MyUrlProvider";
+
+    public UrlInfo? GetUrl(IPublishedContent content, UrlMode mode, string? culture, Uri current)
+        => null;
+
+    public IEnumerable<UrlInfo> GetOtherUrls(int id, Uri current)
+        => [];
+
+    public async Task<UrlInfo?> GetPreviewUrlAsync(IContent content, string? culture, string? segment)
+    {
+        var token = await GetPreviewTokenAsync();
+        return new UrlInfo(
+                url: new Uri($"https://my.preview.environment/?id={content.Key}&culture={culture}&token={token}"),
+                provider: Alias,
+                culture: culture,
+                message: null,
+                isExternal: true);
+    }
+
+    private async Task<string> GetPreviewTokenAsync()
+    {
+        // this is where you'll perform auth against the external preview environment and return an auth token
+    }
+}
+```
+{% endcode %}
+
+The URL provider must be registered with Umbraco using a composer:
+
+{% code title="MyUrlProvider.cs" lineNumbers="true" %}
+```csharp
+using Umbraco.Cms.Core.Composing;
+
+namespace My.Site;
+
+public class MyUrlProviderComposer : IComposer
+{
+    public void Compose(IUmbracoBuilder builder)
+        => builder.AddUrlProvider<MyUrlProvider>();
+}
+```
+{% endcode %}
+
+## Client-side implementation
+
+On the client side, you'll need an extension of:
+
+- Type: `workspaceActionMenuItem`.
+- Kind: `previewOption`.
+
 {% hint style="info" %}
-Support for configuring additional preview environments in the Content Delivery API was introduced in version 12.3.
+You can read more about extensions in the [Extending the Umbraco Backoffice](https://docs.umbraco.com/welcome/getting-started/developing-websites-with-umbraco/extending-the-umbraco-backoffice) article.
 {% endhint %}
 
+Here's a sample extension:
+
+```json
+{
+  "name": "My UrlProvider",
+  "alias": "My.UrlProvider",
+  "extensions": [
+    {
+      "type": "workspaceActionMenuItem",
+      "kind": "previewOption",
+      "alias": "My.PreviewOption",
+      "name": "My Preview Option",
+      "forWorkspaceActions": "Umb.WorkspaceAction.Document.SaveAndPreview",
+      "weight": 99,
+      "meta": {
+        "icon": "icon-umbraco",
+        "label": "My preview option",
+        "urlProviderAlias": "MyUrlProvider"
+      }
+    }
+  ]
+}
+```
+
+This extension works with the URL provider above because the `urlProviderAlias` of the extension matches the `Alias` of the URL provider.
+
+Save the extension as `umbraco-package.json` in a folder under `App_Plugins` and (re)start the site. The result is a new preview option in a pop-up over the "Save and preview" button:
+
+![External preview options in a pop-up over the "Save and preview" button](images/external-preview-option.png)
+
 {% hint style="info" %}
-An upcoming release of Umbraco will allow users to configure custom preview URLs directly in the backoffice.
+The default "Save and preview" button is also an extension of this type.
+
+In other words, multiple preview options can co-exist. If you have multiple external environments, you can create preview options for all of them.
+
+The extension `weight` determines the order of appearance. A `weight` above 100 will swap the default preview option with the custom one.
 {% endhint %}

17/umbraco-cms/reference/routing/request-pipeline/outbound-pipeline.md

@@ -159,11 +159,16 @@ Umbraco ships with a `DefaultUrlProvider`, which provides the implementation for
 // This one is initialized by default
 public class NewDefaultUrlProvider : IUrlProvider
 {
+    public string Alias => …;
+
     public virtual UrlInfo GetUrl(IPublishedContent content, UrlMode mode, string? culture, Uri current)
     {…}
 
     public virtual IEnumerable<UrlInfo> GetOtherUrls(int id, Uri current)
     {…}
+
+    public virtual Task<UrlInfo?> GetPreviewUrlAsync(IContent content, string? culture, string? segment)
+    {…}
 }
 ```
 
@@ -199,6 +204,10 @@ public interface IUrlProvider
     UrlInfo? GetUrl(IPublishedContent content, UrlMode mode, string? culture, Uri current);
 
     IEnumerable<UrlInfo> GetOtherUrls(int id, Uri current);
+
+    Task<UrlInfo?> GetPreviewUrlAsync(IContent content, string? culture, string? segment);
+
+    public string Alias { get; }
 }
 ```