All grant handlers are now enable by default.

https://github.com/nulab/scala-oauth2-provider/blob/0.15.1/scala-oauth2-core/src/main/scala/scalaoauth2/provider/TokenEndpoint.scala#L11

However, almost services don't use all grant.
All grants are enable is not good security. A service might unintentionally use some grant.

I want to change manually to enable grant to service.