Improve the strict configuration validation (#3809)

pkg/config/v1/common.go

@@ -15,9 +15,23 @@
 package v1
 
 import (
+	"sync"
+
 	"github.com/fatedier/frp/pkg/util/util"
 )
 
+// TODO(fatedier): Due to the current implementation issue of the go json library, the UnmarshalJSON method
+// of a custom struct cannot access the DisallowUnknownFields parameter of the parent decoder.
+// Here, a global variable is temporarily used to control whether unknown fields are allowed.
+// Once the v2 version is implemented by the community, we can switch to a standardized approach.
+//
+// https://github.com/golang/go/issues/41144
+// https://github.com/golang/go/discussions/63397
+var (
+	DisallowUnknownFields   = false
+	DisallowUnknownFieldsMu sync.Mutex
+)
+
 type AuthScope string
 
 const (