Remove rabl dependency (#5894)

* Remove rabl dependency

* Replicate old Oj configuration

app/models/account.rb

@@ -184,6 +184,21 @@ class Account < ApplicationRecord
     @keypair ||= OpenSSL::PKey::RSA.new(private_key || public_key)
   end
 
+  def magic_key
+    modulus, exponent = [keypair.public_key.n, keypair.public_key.e].map do |component|
+      result = []
+
+      until component.zero?
+        result << [component % 256].pack('C')
+        component >>= 8
+      end
+
+      result.reverse.join
+    end
+
+    (['RSA'] + [modulus, exponent].map { |n| Base64.urlsafe_encode64(n) }).join('.')
+  end
+
   def subscription(webhook_url)
     @subscription ||= OStatus2::Subscription.new(remote_url, secret: secret, webhook: webhook_url, hub: hub_url)
   end