There is no HS-supported interface to provide a portal-wide UI modification. The closest two options are traditional "CRM Cards", which can show on the sidebar of any *record* page (so far from any page in the portal, but at least on each individual record). You can have a simple button in your CRM card that then triggers a modal window that can render an arbitrary iframe. Second options is also a CRM Card, but built inside the new "CRM Development Tools", which are more flexible and powerful in various ways but *also* restricted to record pages. More importantly for your purposes, they are tied to private app authentication and thus not compatible (yet) with marketplace based apps.
What people sometimes do for custom UI modifications is build a Chrome extension that provides an appropriate overlay (I don't particular recommend this option, just mentioning that it exitst). As far as I remember it's against the terms of service for a marketplace app to include a Chrome extension (or otherwise inject content in the HubSpot app), but I may misremember and it's only against the conditions for *certification* on the marketplace (either way it'd be pretty fatal to your app, since you'd probably want to be certified).
PS You wrote "visual support attached" but I am not seeing an attachment so not sure how close crm cards could get to your design requirements.
Thank you - this is a very thorough and well-thought-out answer. My research over the weekend has led me to many of the same conclusions.
So is it safe to say that most Marketplace apps (with the exception of those working with CRM records) render the app UI in an external environment separate from the HubSpot UI?
Dave Roma, HubSpot CMS Developer
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