In Spring Security, remember me tokens are validated by comparing them with values stored in the database. Given this, why do we need a secret key for generating the tokens? What additional security does it provide?

This is what i am doing

@Bean
public PersistentTokenBasedRememberMeServices rememberMeServices() {
    PersistentTokenBasedRememberMeServices rememberMeServices =
            new PersistentTokenBasedRememberMeServices("secretKey", userDetailsService, persistentTokenRepository);
    rememberMeServices.setAlwaysRemember(true);
    rememberMeServices.setUseSecureCookie(true);
    rememberMeServices.setTokenValiditySeconds(86400); // 24 horas en segundos
    return rememberMeServices;
}