How do I construct an authenticated HTTP request in Postman?
You can make use of Token authentication but be careful:

From module description:


  Be careful with what paths you expose to Token Authentication, as it is effectively a very simple, very low security password mechanism. You can expose Administration pages through bad configuration.



Install / enable Token authentication Module.
Go to admin/config/services/tokenauth
Add the path you want to give access to with token.

in the example below i added all add content pages.
Go to admin/people edit the user you want to generate token.
Generate Token by clicking on Token authentication tab it will give a token for that user like ?token=tuvj7cMwauxStWGVQYfo.
Then you can use it with postman.



Note: it may not be the best way.