Es la ruta donde estará disponible el cookie "/" significa que sera ene todo el dominio
El manual
Cita: The path on the server in which the cookie will be available on. If set to '/', the cookie will be available within the entire domain . If set to '/foo/', the cookie will only be available within the /foo/ directory and all sub-directories such as /foo/bar/ of domain . The default value is the current directory that the cookie is being set in.
Después de eso si puedes mandar el header
Saludos!