This repository shows an example, of how to automatically create a valid idToken in Postman, before requests and use it as a bearer token.
The attached PostmanCollection.json executes a script which invokes the emulated Authenticatior api to create a user. The script is also available here: postman/src/pre-request_script.ts.
When you import the PostmanCollection.json into your Postman workspace you need to set the apiKey. (In order to have an apiKey, you need to create an App in Firebase).
You also need to generate and download the serviceAccountKey.json to the functions folder from the Project settings, Service accounts tab.
After this to setps, you should be able to run the HelloWorld method, which validates the token and returns the user data.
The created user should be visible in the Emulator UI.