Pull request: HOFTIX-csrf

Merge in DNS/adguard-home from HOFTIX-csrf to master

Squashed commit of the following:

commit 75ab27bf6c52b80ab4e7347d7c254fa659eac244
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Sep 29 18:45:54 2022 +0300

    all: imp cookie security; rm plain-text apis

internal/aghhttp/header.go

@@ -0,0 +1,22 @@
+package aghhttp
+
+// HTTP Headers
+
+// HTTP header name constants.
+//
+// TODO(a.garipov): Remove unused.
+const (
+	HdrNameAcceptEncoding           = "Accept-Encoding"
+	HdrNameAccessControlAllowOrigin = "Access-Control-Allow-Origin"
+	HdrNameContentType              = "Content-Type"
+	HdrNameContentEncoding          = "Content-Encoding"
+	HdrNameServer                   = "Server"
+	HdrNameTrailer                  = "Trailer"
+	HdrNameUserAgent                = "User-Agent"
+)
+
+// HTTP header value constants.
+const (
+	HdrValApplicationJSON = "application/json"
+	HdrValTextPlain       = "text/plain"
+)