One of the first things you do when creating a new Symfony 2 project is setting your "secret". This secret string is 40 random characters that is used for CSRF protection.
It would be nice if Symfony just generated one for you. I can't imagine how many projects use the secret key ThisTokenIsNotSoSecretChangeIt.
On load this page generates a string consisting of 40 random hex characters. Feel free to load it whenever you need a new secret key.
From the Symfony docs:
This is a string that should be unique to your application. In practice,
it's used for generating the CSRF tokens, but it could be used in any other
context where having a unique string is useful. It becomes the service container