Zendesk JWT how to send custom data?

Hello!
We have a closed common info on Help Center for our customers. We use Zendesk SSO JWT for authorization from https://support.zendesk.com/hc/en-us/articles/203663816#topic_w5x_1fh_3fb link and it works correctly, but in code, we have to provide a static name/email for payload. Like in example code. We'd like to allow every customer to log in with their own name/email. Customers open https://sub-domain.zendesk.com/ and I'd like to send some custom data (ex. customer_id) to catch which one sends a request on our side. How can I do it

Thank you! 

payload = {
    "iat": int(time.time()),
    "jti": str(uuid.uuid1()),
    "name": "Test Test",
    "email": "test@test.com"
}

shared_key = settings.ZENDESK_SHARED_KEY
jwt_string = jwt.encode(payload, shared_key)