Add back required method

server/callback.go

@@ -16,6 +16,10 @@ type CallbackRequestBuilder struct {
 	}
 }
 
+func (rb CallbackRequestBuilder) RequestBuilder() router.RequestBuilder {
+	return &rb
+}
+
 func (rb *CallbackRequestBuilder) Values(values router.Values) (errRes router.ErrorResponse) {
 	err := rb.values.Values.Parse(values)
 	if err != nil {

server/token.go

@@ -17,6 +17,10 @@ type TokenRequestBuilder struct {
 	}
 }
 
+func (rb TokenRequestBuilder) RequestBuilder() router.RequestBuilder {
+	return &rb
+}
+
 func (rb *TokenRequestBuilder) Values(values router.Values) (errRes router.ErrorResponse) {
 	err := rb.values.Values.Parse(values)
 	if err != nil {