Merge pull request #30583 from nickhudkins/feat/uri-allowlist

feat(sanitizer): add support for allowlisting additional URI protocols

docs/features/techdocs/how-to-guides.md

@@ -606,6 +606,25 @@ techdocs:
 
 This way, custom element like `<backstage-element attribute1="value"></backstage-element>` will be allowed in the result HTML.
 
+## How to allow additional URI protocols in TechDocs
+
+TechDocs uses the [DOMPurify](https://github.com/cure53/DOMPurify) library to
+sanitize HTML and prevent XSS attacks.
+
+It's possible to allow additional URI protocols based on a list of protocols. To do
+this, add the allowed protocols in the `techdocs.sanitizer.additionalAllowedURIProtocols`
+and `additionalAllowedURIProtocols` configuration of your `app-config.yaml`.
+
+For example:
+
+```yaml
+techdocs:
+  sanitizer:
+    additionalAllowedURIProtocols: ["vscode"],
+```
+
+This way, links like `<a href="vscode://settings/">VSCode Settings<a>` will be allowed in the result HTML
+
 ## How to render PlantUML diagram in TechDocs
 
 PlantUML allows you to create diagrams from plain text language. Each diagram description begins with the keyword - (@startXYZ and @endXYZ, depending on the kind of diagram). For UML Diagrams, Keywords @startuml & @enduml should be used. Further details for all types of diagrams can be found at [PlantUML Language Reference Guide](https://plantuml.com/guide).