Add option to disable easy to abuse API endpoints (#5630)

* Add option to disable easy to abuse API endpoints

The API endpoints that will be disabled when this option are:
 - /api/v1/videos
 - /api/v1/clips
 - /api/v1/transcripts

There is still API endponts that need some sort of validation or
connection/proxying to Invidious companion like
`/api/v1/captions` and `/api/v1/storyboards` since they also do a video
request to Invidious companion. I'm not sure if the `/next` API endpoint
could be used to gather that type of information, if so, that would be
better.

Closes #5599

* Rename configuration variable, add additional comment for the option

src/invidious.cr

@@ -217,6 +217,7 @@ end
 Kemal.config.powered_by_header = false
 add_handler FilteredCompressHandler.new
 add_handler APIHandler.new
+add_handler DisableAbusableAPIHandler.new
 add_handler AuthHandler.new
 add_handler DenyFrame.new
 

src/invidious/config.cr

@@ -183,6 +183,9 @@ class Config
   # Playlist length limit
   property playlist_length_limit : Int32 = 500
 
+  # Disable easy to abuse API endpoints
+  property disable_abusable_api : Bool = false
+
   def disabled?(option)
     case disabled = CONFIG.disable_proxy
     when Bool

src/invidious/helpers/handlers.cr

@@ -133,6 +133,26 @@ class APIHandler < Kemal::Handler
   end
 end
 
+class DisableAbusableAPIHandler < Kemal::Handler
+  {% for method in %w(GET HEAD) %}
+    # This endpoints make a video request to Invidious companion.
+    {% for endpoint in %w(videos clips transcripts) %}
+      only ["/api/v1/{{ endpoint.id }}/:id"], {{ method }}
+    {% end %}
+  {% end %}
+
+  def call(env)
+    return call_next env unless only_match?(env) && CONFIG.disable_abusable_api
+
+    env.response.content_type = "application/json"
+    env.response.status_code = 403
+    message = {"error" => "This API endpoint has been disabled by the administrator."}.to_json
+    env.response.print message
+    env.response.close
+    return
+  end
+end
+
 class DenyFrame < Kemal::Handler
   exclude ["/embed/*"]