Building a canvas app in teams (earlier code name project Oakdale) gives you the possibility to create a canvas app in Teams for Teams. More information here
A lot of citizen developers, taken their first steps in developing apps in Teams and they are using also know tools, like SharePoint. But indeed, there is a but. Last week, I had a citizen developer, that was trying to add the SharePoint connector to the canvas app in the editor in Teams and he came into a loop, giving his credentials. But could not select a SharePoint site.
Let us go throw the steps, where the citizen developer gets stuck for adding the SharePoint connector:

Click “Add Data”

Search for “SharePoint”, select and click. This opens a web browser page towards the connectors list:

They clicked the plus sign at the “SharePoint”- connector.

Clicking “Create”

Login

The connection has been added but isn’t visible in the canvas app and currently the only way to do this is this:
Open make.powerapps.com by pressing the link icon.

Go to the Power Apps admin portal, https://admin.powerplatform.microsoft.com/, Environments and search for an environment of the type Microsoft Teams.

Select it and open by clicking the app link in Microsoft Teams association.

This will open the Teams websites and click “use the web app instead”. Do the same as in the Teams desktop client by opening Power Apps and selecting the tab “Build” and open the app.

Search for the SharePoint connector, now it will show the already made connection and the possibility to select a site link.



In the browser the connection will be visible under data. Saving the app and opening it again in Microsoft Teams desktop version.



The permission pop-up will ask to allow the connector and he will be available in the data view. The data in the SharePoint list will be available for the Canvas App from the Microsoft Teams Desktop embedded editor.
Hope this the can help you in your citizen developer journey!