Add ServeHTTP() method to swappableMux struct

Co-authored-by: Roberto Abdelkader Martínez Pérez <robertomartinezp@gmail.com>

internal/server/user/mux.go

@@ -1,6 +1,7 @@
 package user
 
 import (
+	"net/http"
 	"sync"
 
 	"github.com/gorilla/mux"
@@ -8,18 +9,22 @@ import (
 
 type swappableMux struct {
 	m    sync.RWMutex
-	root mux.Router
+	root *mux.Router
 }
 
-func (sm *swappableMux) get() mux.Router {
+func (sm *swappableMux) get() *mux.Router {
 	sm.m.RLock()
 	defer sm.m.RUnlock()
 
 	return sm.root
 }
 
-func (sm *swappableMux) set(mux mux.Router) {
+func (sm *swappableMux) set(mux *mux.Router) {
 	sm.m.Lock()
 	sm.root = mux
 	sm.m.Unlock()
 }
+
+func (sm *swappableMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	sm.get().ServeHTTP(w, r)
+}