register.js

// REGISTER USER WITH REQUIRED CUSTOM CLAIMS
exports.registerUser = functions.https.onCall(async (data, context) => {

    const email = data.email;
    const password = data.password;
    const displayName = data.displayName;

    if (email == null || password == null || displayName == null) {
        throw new functions.https.HttpsError('signup-failed', 'missing information');
    }

    try {
        var userRecord = await admin.auth().createUser({
            email: email,
            password: password,
            displayName: displayName
        });

        const customClaims = {
            "https://hasura.io/jwt/claims": {
                "x-hasura-default-role": "user",
                "x-hasura-allowed-roles": ["user"],
                "x-hasura-user-id": userRecord.uid
            }
        };

        await admin.auth().setCustomUserClaims(userRecord.uid, customClaims);
        return userRecord.toJSON();

    } catch (e) {
        throw new functions.https.HttpsError('signup-failed', JSON.stringify(error, undefined, 2));
    }
});