Ability to disable "Special Use Domain Name" blocking

config/sudn.go

@@ -11,12 +11,12 @@ type SUDN struct {
 	// upstream or custom DNS, which come before SUDN in the resolver chain.
 	// Thus defaulting to `true` and returning NXDOMAIN here should not conflict.
 	RFC6762AppendixG bool `yaml:"rfc6762-appendixG" default:"true"`
+	Enable           bool `yaml:"enable" default:"true"`
 }
 
 // IsEnabled implements `config.Configurable`.
 func (c *SUDN) IsEnabled() bool {
-	// The Special Use RFCs are always active
-	return true
+	return c.Enable
 }
 
 // LogConfig implements `config.Configurable`.

config/sudn_test.go

@@ -18,9 +18,27 @@ var _ = Describe("SUDNConfig", func() {
 	})
 
 	Describe("IsEnabled", func() {
-		It("is true", func() {
+		It("should be true by default", func() {
 			Expect(cfg.IsEnabled()).Should(BeTrue())
 		})
+
+		When("enabled", func() {
+			It("should be true", func() {
+				cfg := SUDN{
+					Enable: true,
+				}
+				Expect(cfg.IsEnabled()).Should(BeTrue())
+			})
+		})
+
+		When("disabled", func() {
+			It("should be false", func() {
+				cfg := SUDN{
+					Enable: false,
+				}
+				Expect(cfg.IsEnabled()).Should(BeFalse())
+			})
+		})
 	})
 
 	Describe("LogConfig", func() {

docs/config.yml

@@ -337,6 +337,7 @@ specialUseDomains:
   # optional: block recomended private TLDs
   # default: true
   rfc6762-appendixG: true
+  enable: true
 
 # optional: configure extended client subnet (ECS) support
 ecs: