Add method implementation for Gateway#authorize

app/models/solidus_paypal_braintree/gateway.rb

@@ -11,6 +11,10 @@ class Gateway < ::Spree::PaymentMethod
       submit_for_settlement: true
     }.freeze
 
+    PAYPAL_AUTHORIZE_OPTIONS = {
+      store_in_vault_on_success: true
+    }.freeze
+
     # This is useful in feature tests to avoid rate limited requests from
     # Braintree
     preference(:client_sdk_enabled, :boolean, default: true)
@@ -35,8 +39,14 @@ def purchase(money, source, _gateway_options)
     end
 
     # @return [Response]
-    def authorize(_money, _source, _gateway_options)
-      raise NotImplementedError
+    def authorize(money, source, _gateway_options)
+      result = ::Braintree::Transaction.sale(
+        amount: money,
+        payment_method_nonce: source.nonce,
+        options: PAYPAL_AUTHORIZE_OPTIONS
+      )
+
+      Response.build(result)
     end
 
     # @return [Response]

spec/models/solidus_paypal_braintree/gateway_spec.rb

@@ -57,6 +57,19 @@
     end
   end
 
+  describe "#authorize" do
+    subject(:authorize) do
+      gateway.authorize(10.00, source, {})
+    end
+
+    it "returns a successful billing response", aggregate_failures: true do
+      expect(authorize).to be_a ActiveMerchant::Billing::Response
+      expect(authorize).to be_success
+      expect(authorize).to be_test
+      expect(authorize.message).to eq "authorized"
+    end
+  end
+
   describe "#void" do
     subject(:void) { gateway.void(response_code, source, {}) }