This is a string that should be unique to your application and it's commonly used

to add more entropy to security related operations. Its value should be series of

characters, numbers and symbols choosen randomly. It's recommended length is

around 32 characters.

In practice, Symfony uses this value for generating the :ref:`CSRF tokens <forms-csrf>`,

for encrypting the cookies used in the :doc:`remember me functionality </cookbook/security/remember_me>`

and for creating signed URIs when using :ref:`ESI (Edge Side Includes) <edge-side-includes>` .

This option becomes the service container parameter named ``kernel.secret``,

which you can use whenever the application needs a immutable random string

to add more entropy.

As any other security-related parameter, is a good practice to change this

value from time to time. However, keep in mind that changing this value will

invalidate all signed URIs and Remember Me cookies. That's why, after changing

this value, you should regenerate the application cache, delete the HTTP Cache

related cache and log out all the application users.