Force ExplicitForm authentication when SSO is enabled

When SSO is enabled, by default storefront acces is using it instead of the explicit form. And some multi-account users can start grunting. We can force the display of the explicit form by editing the CtxsAuthMethod cookie in ReceiverFolder\custom\script.js :

if( CTXS.getCookie("CtxsAuthMethod")==null){
    CTXS.setCookie("CtxsAuthMethod","ExplicitForms",true);
}