Awesome. Those two blog posts of Chris helped me find the solution:
a combo of relative path and passing along the parameter using Query.
After publishing the .pbix file, I had to set the credentials on the data set to Anonymous as well.
(I pass along an API key in the function itself)
I'm suprised Excel based Web data is not supported.
The M-code calls Excel.Workbook......
Source = Excel.Workbook(Web.Contents("https://research.stlouisfed.org/fred2/graph/fredgraph.xls?chart_type=line&recession_bars=on&log_scal..."), null, true),
Anyone know if this is on the roadmap?