I just updated my projects to the new Google Apps / Firebase console.
Where do I find the secret associated with my account in the new console?
I have added a picture with steps on how to reach this step. You may find this useful https://imgur.com/a/Y2gzD
To see a full list of all the credentials associated with your firebase app you would have to go to
Google Developer Console
On the menu tab select your firebase project from the dropdown menu.
On the Credentials tab you will find all your keys both API keys and OAuth 2.0 client IDs for both browser and server authentications.