Revert "Deprecated `Referer` checking for hotlink prevention in favour of token verification system"

Might not be a good idea to fully remove it right now...

CHANGELOG.md

@@ -11,7 +11,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - [2020-07-04] Changed GitLab CI to build on every push irregardless of tagging by [@carbotaniuman].
 
 ### Deprecated
-- [2020-07-05] Deprecated `Referer` checking for hotlink prevention in favour of token verification system by [@lflare].
 
 ### Removed
 

src/main/kotlin/mdnet/base/server/ImageServer.kt

@@ -135,7 +135,10 @@ class ImageServer(
                 }
             }
 
-            if (snapshot != null && imageDatum != null) {
+            if (request.header("Referer")?.startsWith("https://mangadex.org") == false) {
+                snapshot?.close()
+                Response(Status.FORBIDDEN)
+            } else if (snapshot != null && imageDatum != null) {
                 request.handleCacheHit(sanitizedUri, getRc4(rc4Bytes), snapshot, imageDatum)
             } else {
                 if (snapshot != null) {