vars: Allow overriding `http.auth.user.id` in replacer as a special case (#6108)

1 files changed, 6 insertions, 0 deletions

diff --git a/modules/caddyhttp/vars.go b/modules/caddyhttp/vars.go
index 917a15051..f5afe264a 100644
--- a/modules/caddyhttp/vars.go
+++ b/modules/caddyhttp/vars.go
@@ -57,6 +57,12 @@ func (m VarsMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request, next H
 			v = repl.ReplaceAll(valStr, "")
 		}
 		vars[keyExpanded] = v
+
+		// Special case: the user ID is in the replacer, pulled from there
+		// for access logs. Allow users to override it with the vars handler.
+		if keyExpanded == "http.auth.user.id" {
+			repl.Set(keyExpanded, v)
+		}
 	}
 	return next.ServeHTTP(w, r)
 }