### Issue Description The [`CORSConfig` struct type](https://github.com/labstack/echo/blob/98a523756d875bc13475bcb6237f09e771cbe321/middleware/cors.go#L14) has the following [field](https://github.com/labstack/echo/blob/98a523756d875bc13475bcb6237f09e771cbe321/middleware/cors.go#L42): ```go AllowOriginFunc func(origin string) (bool, error) `yaml:"allow_origin_func"` ``` The field tag puzzles me. How is such a function meant to be unmarshalled from YAML? ### Checklist - [x] Dependencies installed - [x] No typos - [x] Searched existing issues and docs ### Version/commit v4.11.2