The interface specification for the restful API is available online at: http://transparency.entsoe.eu/content/static_content/Static%20content/web%20api/Guide.html
Please follow the steps below so as to get the access granted:
1. Register on Transparency Platform.
2. Request access to Rest API by sending email to firstname.lastname@example.org .
Please indicate the email address with which you have registered.
3. After our confirmation that access has been granted, login to Production platform
4. Check your Account Settings. The Security Token should be visible under "Web Api Security Token"