Add token_lookup_batch_size config option

In case you enabled `reuse_access_token` option Doorkeeper will try to find matching
token using `matching_token_for` Access Token API that searches for valid records
in batches in order not to pollute the memory with all the database records. By default
Doorkeeper uses batch size of 10 000 records. You can increase or decrease this value
depending on your needs and server capabilities.

```ruby
token_lookup_batch_size 10_000
```

lib/doorkeeper/config.rb

@@ -268,6 +268,7 @@ def configure_secrets_for(type, using:, fallback:)
     option :active_record_options,          default: {}
     option :grant_flows,                    default: %w[authorization_code client_credentials]
     option :handle_auth_errors,             default: :render
+    option :token_lookup_batch_size,        default: 10_000
 
     # Allows to customize OAuth grant flows that +each+ application support.
     # You can configure a custom block (or use a class respond to `#call`) that must

lib/doorkeeper/models/access_token_mixin.rb

@@ -126,8 +126,9 @@ def find_matching_token(relation, application, scopes)
         return nil unless relation
 
         matching_tokens = []
+        batch_size = Doorkeeper.configuration.token_lookup_batch_size
 
-        find_access_token_in_batches(relation) do |batch|
+        find_access_token_in_batches(relation, batch_size: batch_size) do |batch|
           tokens = batch.select do |token|
             scopes_match?(token.scopes, scopes, application.try(:scopes))
           end

lib/generators/doorkeeper/templates/initializer.rb

@@ -117,6 +117,14 @@
   #
   # reuse_access_token
 
+  # In case you enabled `reuse_access_token` option Doorkeeper will try to find matching
+  # token using `matching_token_for` Access Token API that searches for valid records
+  # in batches in order not to pollute the memory with all the database records. By default
+  # Doorkeeper uses batch size of 10 000 records. You can increase or decrease this value
+  # depending on your needs and server capabilities.
+  #
+  # token_lookup_batch_size 10_000
+
   # Set a limit for token_reuse if using reuse_access_token option
   #
   # This option limits token_reusability to some extent.

spec/lib/config_spec.rb

@@ -641,6 +641,21 @@ class FakeCustomModel; end
     end
   end
 
+  describe "token_lookup_batch_size" do
+    it "uses default doorkeeper value" do
+      expect(subject.token_lookup_batch_size).to eq(10_000)
+    end
+
+    it "can change the value" do
+      Doorkeeper.configure do
+        orm DOORKEEPER_ORM
+        token_lookup_batch_size 100_000
+      end
+
+      expect(subject.token_lookup_batch_size).to eq(100_000)
+    end
+  end
+
   describe "strict_content_type" do
     it "is false by default" do
       expect(subject.enforce_content_type).to eq(false)