Add an account endpoint for ActivityPub and link to it on HTML profile pages

app/controllers/api/activitypub/accounts_controller.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class Api::Activitypub::AccountsController < ApiController
+  before_action -> { doorkeeper_authorize! :read }, except: [:show]
+  before_action :require_user!, except: [:show]
+  before_action :set_account, except: [:verify_credentials, :suggestions, :search]
+
+  respond_to :'application/activity+json'
+  respond_to :'application/ld+json; profile="https://www.w3.org/ns/activitystreams#"'
+
+  def show
+    render content_type: :'application/ld+json; profile="https://www.w3.org/ns/activitystreams#"'
+  end
+
+  private
+
+  def set_account
+    @account = Account.find(params[:id])
+  end
+end