fix routing issue for esoteric characters in gorilla/mux (#8967)

First step is to ensure that Path component is not decoded
by gorilla/mux to avoid routing issues while handling
certain characters while uploading through PutObject()

Delay the decoding and use PathUnescape() to escape
the `object` path component.

Thanks to @buengese and @ncw for neat test cases for us
to test with.

Fixes #8950
Fixes #8647

cmd/logger/audit.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/url"
 	"time"
 
 	"github.com/gorilla/mux"
@@ -143,7 +144,10 @@ func AuditLog(w http.ResponseWriter, r *http.Request, api string, reqClaims map[
 
 	vars := mux.Vars(r)
 	bucket := vars["bucket"]
-	object := vars["object"]
+	object, err := url.PathUnescape(vars["object"])
+	if err != nil {
+		object = vars["object"]
+	}
 
 	// Send audit logs only to http targets.
 	for _, t := range AuditTargets {