Turns out that issue was something else which I fixed. But for some reason when I call the method, it runs, but when I close the browser and go back to the page, I'm logged out.

This is the code I'm using:

// Set view mode to live site after login to prevent bar with "Close preview mode"
CMSContext.ViewMode = CMS.PortalEngine.ViewModeEnum.LiveSite;

// Ensure response cookie
CookieHelper.EnsureResponseCookie(FormsAuthentication.FormsCookieName);



if (Membership.ValidateUser(userEmail, customerPwd))
{
FormsAuthentication.SetAuthCookie(userEmail, false);
CMS.GlobalHelper.RequestStockHelper.Remove("CurrentUser");
CMS.GlobalHelper.RequestStockHelper.Add("CurrentUser", new CMS.CMSHelper.CurrentUserInfo(ui, true));
}

// Set cookie expiration
if (RememberMeSet)
{
CookieHelper.ChangeCookieExpiration(FormsAuthentication.FormsCookieName, DateTime.Now.AddYears(1), false);
}
else
{
FormsAuthentication formAuth = new FormsAuthentication();
// Extend the expiration of the authentication cookie if required
if (!UserInfoProvider.UseSessionCookies && (HttpContext.Current != null) && (HttpContext.Current.Session != null))
{
CookieHelper.ChangeCookieExpiration(FormsAuthentication.FormsCookieName, DateTime.Now.AddMinutes(HttpContext.Current.Session.Timeout), false);
}
}