Allow to override HTTP transport by custom one

adyen.go

@@ -37,6 +37,7 @@ const (
 //       - Credentials instance of API creditials to connect to Adyen API
 //       - Currency is a default request currency. Request data overrides this setting
 //       - MerchantAccount is default merchant account to be used. Request data overrides this setting
+//       - client is http client instance
 //
 // Currency and MerchantAccount should be used only to store the data and be able to use it later.
 // Requests won't be automatically populated with given values
@@ -117,6 +118,13 @@ func WithTimeout(d time.Duration) func(*Adyen) {
 	}
 }
 
+// WithTransport allows customer HTTP transports to be provider to the Adyen
+func WithTransport(transport http.RoundTripper) func(*Adyen) {
+	return func(a *Adyen) {
+		a.client.Transport = transport
+	}
+}
+
 // WithCurrency allows for custom currencies to be provided to the Adyen.
 func WithCurrency(c string) func(*Adyen) {
 	return func(a *Adyen) {