Function grant_role 

pub async fn grant_role<T: Transport + ?Sized>(
    transport: &T,
    community: &Community,
    member: PublicKey,
    role_id: &str,
) -> Result<(), String>

Grant member a role (requires the MANAGE_ROLES permission). Publishes the per-member Grant event. The member already holds read keys from membership; the roster entry adds write authority, exercised by signing their own control actions, which peers verify against the roster.