caddyauth: Add Metadata field to caddyauth.User (#3174)

* caddyauth: Add Metadata field to caddyauth.User

* Apply gofmt

* Tidy it up a bit

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>

modules/caddyhttp/caddyauth/caddyauth.go

@@ -77,7 +77,10 @@ func (a Authentication) ServeHTTP(w http.ResponseWriter, r *http.Request, next c
 	}
 
 	repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
-	repl.Set("http.authentication.user.id", user.ID)
+	repl.Set("http.auth.user.id", user.ID)
+	for k, v := range user.Metadata {
+		repl.Set("http.auth.user."+k, v)
+	}
 
 	return next.ServeHTTP(w, r)
 }
@@ -92,7 +95,15 @@ type Authenticator interface {
 
 // User represents an authenticated user.
 type User struct {
+	// The ID of the authenticated user.
 	ID string
+
+	// Any other relevant data about this
+	// user. Keys should be adhere to Caddy
+	// conventions (snake_casing), as all
+	// keys will be made available as
+	// placeholders.
+	Metadata map[string]string
 }
 
 // Interface guards