Magento 2 – Minicart Not Updated After Login from Authentication Popup

Thanks for your help :)

I have found how to trigger it, you need to set up a sections.xml inside etc/frontend of your module that tells Magento which sections to update for a given Ajax call. Here is an example;

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Customer:etc/sections.xsd">
    <action name="[frontName]/[ActionPath]/[ActionName]">
        <section name="cart"/>
    </action>
</config>

After my Ajax call has finished to [frontName]/[ActionPath]/[ActionName] Magento makes another call to /customer/section/load passing the sections to load.

By default it requests any messages but if you have set up your sections.xml correctly you will also see the section names you have defined in there as well.

You said guest checkout is enabled in your system but authentication pop up doesn't appear when you have guest checkout enabled. Go to Stores->Configuration->Sales->Checkout. Under Checkout options make sure Guest checkout is set to yes. Authentication pop up can also appear if your cart has a digital product.

Now to answer your question as to how to redirect customer where he intended to go: Overide Magento_Customer/js/view/authentication-popup.js with your theme or custom module. Line that will interest you is

if ($(loginForm).validation() &&
    $(loginForm).validation('isValid')
) {
  this.isLoading(true);
  loginAction(loginData, null, false);
}

Pass your redirect url instead of null to loginAction function. You will find implementation of loginAction in file vendor/magento/module-customer/view/frontend/web/js/action/login.js.

You can decide your redirect url based on which button was clicked. Hope that helps.