The route proxy tells a backend the request was HTTPS, and for which name

NewSingleHostReverseProxy sets only X-Forwarded-For, so a backend that writes its own addresses saw
the plain hop from the proxy: Gitea's Go import tag named an http clone URL and go get refused the
SDK's module path. The proxy now sets X-Forwarded-Proto, -Host and -For from the request it received,
and keeps the Host header as it was.

examples/route-proxy/main.go

@@ -273,7 +273,7 @@ func (t *table) set(routes map[string][]rule, public map[string]bool) {
 				log.Printf("route %s points at %q, which is not a URL: %v", host, r.target, err)
 				continue
 			}
-			r.to = httputil.NewSingleHostReverseProxy(where)
+			r.to = towards(where)
 			if r.insecure {
 				r.to.Transport = &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}}
 			}
@@ -1060,3 +1060,17 @@ func asPort(v any) (int, bool) {
 	}
 	return 0, false
 }
+
+// towards proxies to one backend and tells it what the client asked: **X-Forwarded-Proto, -Host and
+// -For**, set from the request this proxy received. A backend that builds its own addresses — a forge
+// writing its clone URL into a page, a login redirect — otherwise sees the plain HTTP hop from this
+// proxy and writes `http://`, though every client reached it over TLS: Go refused the forge's module
+// path for exactly that on 2026-10-03, its import tag naming an http clone URL.
+// The standard library's NewSingleHostReverseProxy sets only X-Forwarded-For.
+func towards(where *url.URL) *httputil.ReverseProxy {
+	return &httputil.ReverseProxy{Rewrite: func(pr *httputil.ProxyRequest) {
+		pr.SetURL(where)
+		pr.Out.Host = pr.In.Host
+		pr.SetXForwarded()
+	}}
+}