Check the codes on login with a simple if statement
if{code1 == "edgwreggw" || code2 == "etgwg"....)
{
FormsAuthentication.RedirectFromLoginPage(data.username, true);
}
else
{
login fail
}
Webconfig
<authentication mode="Forms">
<forms loginUrl="~/UserAuthentication/SignIn" timeout="10" defaultUrl="~\Home\Index" />
</authentication>