Azure Front Door Remove Trailing Slashes for Directory Origin

Question

I am trying to remove trailing slashes in Azure Front Door

So if I user loads contoso.com/foo

they will be shown the page at: origin.azurewebsites.net/foo/index.html

But currently the source azure web app is redirecting from /foo to /foo/ per standard IIS rules

So requests for contoso.com/foo/ load fine however requests for contoso.com/foo redirect to origin.azurewebsites.net/foo/

I am trying to solve this in Front Door with:

Patterns to match:
/foo
/foo/
/bar
/bar/

Origin Path: Empty

and

Rule Set:

If Condition | Equal | /foo /foo/
Then 
Source Pattern: /
Destination /foo/index.html
Preserve Unmatched Path: No

However the rewritten url goes to:

origin.azurewebsites.net/fooindex.html

I've tried changing many things in this setup but can't find the solution

If I remove index.html then it simply rewrites to origin.azurewebsites.net/foo which redirects to origin.azurewebsites.net/foo/