How to create a user immediately with a role without overriding default methods in Loopback?

Question

MongoDB

I inherited the model

{
  "name": "user",
  "plural": "users",
  "base": "User",
  "relations": {
    "roles": {
      "type": "hasMany",
      "model": "Role",
      "foreignKey": "principalId",
      "through": "RoleMapping"
    }
  }
}

Can I immediately associate it with the role without redefining custom remote methods?
Well, that is, in order not to write something like
create a user -> take a user instance -> bind a role
Because I know that in the loopback out of the box there are a lot of interesting things like includes, etc., so for sure it automatically makes such transactions
what the body should be request?