Derive the entrypoint URL scheme from the shared TLS predicate (closes #272)

internal/handlers/source_management.go

@@ -13,6 +13,7 @@ import (
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/delivery"
+	"sneak.berlin/go/webhooker/internal/reqtls"
 )
 
 // WebhookListItem holds data for the webhook list view.
@@ -427,16 +428,16 @@ func (h *Handlers) renderSourceDetail(
 		}
 	}
 
-	host := r.Host
-	scheme := "https"
-
-	if r.TLS == nil {
-		scheme = "http"
+	scheme := "http"
+	if reqtls.IsTLS(r) {
+		scheme = "https"
 	}
 
-	if fwdProto := r.Header.Get("X-Forwarded-Proto"); fwdProto != "" {
-		scheme = fwdProto
-	}
+	// The host is the client's Host header, unvalidated. It is
+	// inert only because source_detail.html renders BaseURL as
+	// text inside a <code> element; putting it in an href or any
+	// other URL context needs it constrained first.
+	baseURL := scheme + "://" + r.Host
 
 	// The template calls Webhook methods, which take pointer
 	// receivers; html/template cannot address a value stored in a map.
@@ -448,7 +449,7 @@ func (h *Handlers) renderSourceDetail(
 		"Entrypoints": NewEntrypointViews(entrypoints),
 		"Targets":     delivery.NewTargetViews(targets),
 		"Events":      events,
-		"BaseURL":     scheme + "://" + host,
+		"BaseURL":     baseURL,
 	}
 
 	h.renderTemplate(w, r, "source_detail.html", data)