[keycloak-user] KeyCloak customization

Hi Can any suggest I am looking to customize /token service for password grant..so when i call /token service from my client,keycloak calls my authentication service to authenticate the user and take the response from my auth service and then tie this response with the access token.. And when i call the secured service with the access token..keycloak can fetch specific user information from my db using access token (which we tied with auth response earlier) and stuff it in request before sending it to secured api.. Can i achieve this and what hooks or customizations i need to do for this Thanks Amit