XHTTP transport: New options for bypassing CDN's detection (#5414)

Usage: https://github.com/XTLS/Xray-core/pull/5414#issuecomment-3770071786

Closes https://github.com/XTLS/Xray-core/issues/4346

---------

Co-authored-by: 风扇滑翔翼 <Fangliding.fshxy@outlook.com>

transport/internet/tls/ech.go

@@ -257,7 +257,8 @@ func dnsQuery(server string, domain string, sockopt *internet.SocketConfig) ([]b
 		}
 		req.Header.Set("Accept", "application/dns-message")
 		req.Header.Set("Content-Type", "application/dns-message")
-		req.Header.Set("X-Padding", strings.Repeat("X", int(crypto.RandBetween(100, 1000))))
+		req.Header.Set("X-Padding", utils.H2Base62Pad(crypto.RandBetween(100, 1000)))
+
 		resp, err := client.Do(req)
 		if err != nil {
 			return nil, 0, err