I've got REST webservice based on Grails. There's obligatory authentication before you can access any page except login. 
I use Geb & Spock for integration tests, running through Gradle. My question is: how can I provide authentication before executing any test?
I have 2 ideas:

1. Run tests in order (log in at first, then run others). How? (must be triggering by command `gradle integrationTest`)
2. Execute JS script before every test which authenticate me. How to implement this in test?