Requirement: A Power Apps Portal that has an embedded Power BI report, and depending on who is looking at it, it shows different data.
Example: a 'support portal' that multiple clients login to, and see a report based on their tickets, but we don't need to create a portal per client, the dashboard auto filters to just show their data.
Currently: Power App Portals shows it supports RLS (Role Level Security) from Power BI using their new language "Liquid Template", but what it actually does is uses the integration/developer's account, not the portal users' account. For example, our developer John embeds a the support Power BI into the Portal, then Client ABC logs in, and they look at the report, and it shows them all client data, because the Power BI is receiving John's username, not Client ABC's user.
Confirmation: We have spoken extensively to various Microsoft teams including a direct link to the Liquid Template developers, and this is currently expected functionality, so that Power BI uses the developers' (John from examples) Power BI licence, and saves all the external users being licenced. However, by using John's username, we cannot detect which user is viewing it, and cannot filter the report accordingly.
The Microsoft developers have advised if we can get some backing to this idea in the uservoice forum, they'll be able to prioritise it in the development backlog.
In summary. Microsoft, please continue to develop the Liquid Template Language and Power Apps Portals to allow this functionality of filtered Power BI reports based on Portal users.