Dynamically set X-Hasura-role in the claim with Firebase

I'm using Hasura as my backend and Google's Firebase for auth in a React app. I have the following roles and constructs:

• Manager - these are my paying customers. They can own 1 or more Team.
• Employee - these are just normal users. They must be invited to be part of a Team by a Manager via email

Both Manager and Employee can sign in / sign up using their Google account or their own email/password.

I have the GraphQL models all set up with the correct relationship and everything. The only thing I can't figure out is how to set the x-hasura-role in Firebase function's hook.

How do I put business logic in this snippet? (i.e. how do I distinguish the Manager from the Employee role)

exports.processSignUp = functions.auth.user().onCreate(user => {
    const customClaims = {
        "https://hasura.io/jwt/claims": {
            "x-hasura-default-role": "manager",
            "x-hasura-allowed-roles": ["manager"], // ????????? how to check "employee"?
            "x-hasura-user-id": user.uid
        }
    };

    ...
})