Pre-request Scripts in Postman | The Exploratory

You can use pre-request scripts in Postman to execute JavaScript before a request runs. By including code in the Pre-request Script tab for a request, collection, or folder, you can carry out pre-processing such as setting variable values, parameters, headers, and body data.

Docs: https://learning.postman.com/docs/wri...

Public Workspace: https://www.postman.com/twitter/works...
For an example of a collection making use of pre-request scripts, check out Twitter’s public workspace in the link above. They use pre-request scripts at the collection level to handle authentication.

Blog:   / how-to-automate-oauth2-token-renewal-in-po...  
For an advanced and practical use case using pre-request scripts, check out this blog post by Allen Helton on refreshing OAuth 2.0 tokens.

Presenter: Sean Keegan, Developer Advocate