I am exited to see that Azure AD secured web apis can be used from SPFx web parts
https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/guidance/connect-to-api-secured-with-...
What is not clear is whether this will work with external users. Say I want to add a button (SPFx extension) to a list that calls a web api. Will it work if the current user is signed in with a Microsoft account?
