Add support for configurable DKIM key sizes

app/models/domain.rb

@@ -82,7 +82,7 @@ def parent_domains
   end
 
   def generate_dkim_key
-    self.dkim_private_key = OpenSSL::PKey::RSA.new(1024).to_s
+    self.dkim_private_key = OpenSSL::PKey::RSA.new(Postal::Config.postal.default_dkim_key_size).to_s
   end
 
   def dkim_key

doc/config/yaml.yml

@@ -23,6 +23,8 @@ postal:
   use_local_ns_for_domain_verification: false
   # Append a Resend-Sender header to all outgoing e-mails
   use_resent_sender_header: true
+  # The default size for new DKIM keys
+  default_dkim_key_size: 1024
   # Path to the private key used for signing
   signing_key_path: $config-file-root/signing.key
   # An array of SMTP relays in the format of smtp://host:port

lib/postal/config_schema.rb

@@ -66,6 +66,11 @@ module Postal
         default true
       end
 
+      integer :default_dkim_key_size do
+        description "The default size for new DKIM keys"
+        default 1024
+      end
+
       string :signing_key_path do
         description "Path to the private key used for signing"
         default "$config-file-root/signing.key"