Update authentication.md

Author: bezhermoso

Resources/doc/authentication.md

@@ -16,4 +16,17 @@ Swagger UI Bundle
           realm: "your-realms"
 ```
 
-Coupled with the correct OAuth authentication definition in your API declarations, 
+Coupled with the correct OAuth authentication definition in the Swagger API declarations, an OAuth authentication flow will be presented in the documentation.
+
+### HTTP
+```
+  al_swagger_ui:
+      http:
+          enable: true
+          key_name: __key
+          delivery: query
+```
+
+This will add an API key field in the documentation page. `delivery` can be set to either `query` or `header`, whichever is applicable to your API authentication protocol.
+
+__Note that both of these authentication methods can be enabled at the same time.__