QGIS - connect to ArcGIS FeatureServer hosted behind Azure proxy

Question

I am using the QGIS (v3.16.0) ArcGisFeatureServer tool in the Browser window to try and connect to the following ArcGIS Feature Server: https://gojdippmaps.azurewebsites.net/proxy.ashx?https://maps.gov.je/arcgis/rest/services/Historic_Buildings/Historic_Buildings/FeatureServer

Note that this server requires an http referrer, such as: https://www.gov.je//citizen/Planning/Pages/HistoricEnvironmentDetail.aspx

Note also that the host is gojdippmaps.azurewebsites.net and the https://maps.gov.je.. url is treated as a parameter in the query string (preceded by ? after the path /proxy.ashx).

If I add the url as shown above I get "Connection failed: Network error" from the ArcGisFeatureServer tool. Hovering over this yields the following message:

Error transferring https://gojdippmaps.azurewebsites.net/proxy.ashx?https://maps.gov.je/arcgis/rest/services/Historic_Buildings/Historic_Buildings/FeatureServer&f=json - server replied: Bad Request

This appears to be because QGIS is trying to add f=json as a second parameter to the query string (preceded by &). If I instead make the request in a web browser (using the referrer header above) but replace the & with ? the request is successful.

Question: Is it possible (using the ArcGisFeatureServer tool or otherwise) to connect to this server and add the layer it contains to a QGIS project?

I have no expertise in Azure-hosted web applications and this is the first time I've seen a proxied url in a query string like this treated as a parameter. It appears QGIS cannot correctly deal with this scenario.

Answer 1

I'll comment on the QGIS bug but the short answer is no, and it's going to be a fair amount of work for the QGIS guys to sort this out.

The problem is the double '?' in the query; one for the first proxy and one for the second. I'm not an RFC expert but I don't think that's very kosher, so QUrl and QUrlQuery (what QGIS is using under the hood) are getting a bit confused by the URL we need to use in the dialog.

Very weird hack to at least query the server capabilities is to add a =? to the end of your URL, which tricks QGIS and Qt into making the first MapServer queries at least somewhat correct. However as soon as you try to use one of the new exposed layers it breaks as QGIS needs to add /export, /query, etc. to the URL for interfacing with the arcgis REST stuff.

Anyways, long story short, grab this python script: https://gist.github.com/eresonance/9e3dc8f78dad2c61c38075e9c9657c53

Change the g_redirect_url to be the first part of your arcgis URL (https://gojdippmaps.azurewebsites.net/proxy.ashx) and g_referer_url to be the referer you would use in the headers (https://www.gov.je//citizen/Planning/Pages/HistoricEnvironmentDetail.aspx). Then run that bad boy with python3 in a separate console.

Now you use this as your QGIS URL: http://localhost:9999/https://maps.gov.je/arcgis/rest/services/Historic_Buildings/Historic_Buildings/FeatureServer

And because it doesn't have a ? in it anywhere, QGIS will construct the URL enpoints correctly. Those all get forwarded to the python script, which tacks the Azure proxy back on and adds the desired referer header, then grabs and returns the data from the resulting constructed proxy URL.