[#13] Rename go module name according to NSPCC standards

- refactoring s3 gate structure
- cleanup unused code
- rename go module to `github.com/nspcc-dev/neofs-s3-gate`

closes #13

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

api/user-auth.go

@@ -0,0 +1,25 @@
+package api
+
+import (
+	"net/http"
+
+	"github.com/gorilla/mux"
+	"github.com/nspcc-dev/neofs-s3-gate/auth"
+	"go.uber.org/zap"
+)
+
+func AttachUserAuth(router *mux.Router, center *auth.Center, log *zap.Logger) {
+	uamw := func(h http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			bearerToken, err := center.AuthenticationPassed(r)
+			if err != nil {
+				log.Error("failed to pass authentication", zap.Error(err))
+				WriteErrorResponse(r.Context(), w, GetAPIError(ErrAccessDenied), r.URL)
+				return
+			}
+			h.ServeHTTP(w, r.WithContext(auth.SetBearerToken(r.Context(), bearerToken)))
+
+		})
+	}
+	router.Use(uamw)
+}