If the Contact record has been created for the user, make sure that you either have relevant permissions in the Authenticated Web Role, or a custom Web Role that you assign with a real-time workflow when he Contact is created.
Alternatively, you can check if a User is logged in by using Liquid (probably in the Header or Footer) and if not do a javascript redirect
{% if user %}
Hello, {{ user.fullname | escape }}!
{% else %}
<script>
window.location.href='./SignIn/';
</script>
{% endif %}
