[keycloak-user] OAuth 2.0 Extension Grants?

Sent this in HTMl by accident. Let's try this again.   Does Keycloak (4.0 and up) support custom extension grants?   Relevant section: https://tools.ietf.org/html/rfc6749#section-4.5   Context: My company has a legacy api that rolled its own access token protocol. I want to create a custom grant type that uses our legacy token as credentials for the token endpoint. Thanks in advance, Al