Here's the documentation for setting up the HubSpot chat widget in a client app and for configuring the Visitor Identification API that will allow HubSpot to identify logged-in users and let support know who they're chatting with:
HubSpot chat widget:
First, here's the HubSpot tracking code to install on the app pages; widget won't work otherwise.
Tracking code:
<!-- Start of HubSpot Embed Code -->
<script type="text/javascript" id="hs-script-loader" async defer src="//js.hs-scripts.com/661136.js"></script>
<!-- End of HubSpot Embed Code -->
<script type="text/javascript" id="hs-script-loader" async defer src="//js.hs-scripts.com/661136.js"></script>
<!-- End of HubSpot Embed Code -->
And here's the SDK documentation for configuring widget behavior: https://developers.hubspot.com/docs/api/conversation/chat-widget-sdk
Visitor Identification API:
This API uses the Private App function in HubSpot, so one will have to be created by an Admin.
Here are the documentation links for private apps and the visitor API: