How can I make two domain names work with a heroku app?

I have a heroku app, that is configured with two domain names. Say and My problem is visiting these two domain names show me different results for authentication. Say, if I'm logged in from and then I visit, I will have to re-login at, even though I logged in from

How can I fix this at heroku?. I am a beginner at this. Any help will be appreciated. Please do guide.

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