How do I set cookies within Heroku Review App?

I am managing two separate apps through two different Heroku pipelines.

App 1 - Handles my auth, this is a login landing page. App 2 - The main app, can access after authenticating via App 1.

I have separate review apps running for each app. The reasoning was so I can have both Review Apps under the .herokuapp.com domain.

App 1 takes Username, Password, and sets a JWT. In App 1, a query param is set and it contains a callbackUrl to App2. The JWT is set as a cookie in App 1 and sent to App 2 via a cookie (a token).

This is a problem with the new Same-Site Rules in Chrome. However, I have read various articles and workarounds for this, and my Cookies are still blocked. Here is the error:

the Set-Cookie was blocked because its domain attribute was invalid with regards to the current host url.

I believe they are blocked because the domain .herokuapp.com is on the Public Suffix List, so no matter what I do, they will always be blocked.

Is there a workaround for this? Can I use my own domain with a review app? Ideally:

app1.helloworld.com app2.helloworld.com

.helloworld.com would be the domain.