OAuth UserInfoJson attributes are very restrictive

I am wondering why the attributes property in UserInfoJson is so strictly typed as map[string][]string.

We are working on a project where some additional attributes are passed as map[string]string, which makes sense from a developer perspective.

Is this an OAuth spec or was it added for other reasons?

If it’s not a spec, would you accept a PR, which changes to a more generic typing e.g. map[string]interface{}?