I have configured a form-base authentication using Spring security. It works fine when I log in using the login form in my web application.
It also works with cURL:
Finally I managed making Postman aware of authentication by using the Postman Interceptor chrome extension
With the extension enabled (by clicking the satellite icon within the Postman App), you just need to log in using the login form of your web and then you can start using services that require authentication in Postman.