Proxy is replacing part of address with an empty string

[jmacura]

Bug

Describe the bug
When a path to proxy is provided as a relative path, the proxy incorrectly throws away part of the original address resulting in an invalid URL.

To Reproduce
...

Expected behavior
The URL gets only encoded, no parts are dropped.

Screenshots

Additional context
observable on hub4everybody.com and watlas.lesprojekt.cz

[jmacura]

Discovered so far:

• only happens with hslayers-server on hub4everybody, watlas
• not replicable on localhost
• not replicable with a different type of proxy server
• only happens when the URL is a WMS service from ArcGIS server
• not replicable on non-ArcGIS WMS servers
• the URL returned in GetCapabilities document is changed to the hostname of requesting server (h4e, watlas, ...), i.e. <OnlineResource xmlns:xlink="http://www.w3.org/1999/xlink" xlink:type="simple" xlink:href="https://watlas.lesprojekt.cz/arcgis2/services/dmr4g/ImageServer/WMSServer"/>
• x-forwarded-for , x-forwarded-host and x-forwarded-server HTTP headers are added to the request when sent
• sec-fetch-site HTTP header is cross-site on localhost but same-origin on the public server

[jmacura]

Update:

• seems to be caused by the X-Forwarded-Host HTTP header
• the "xfwd": "false" option in http-proxy seems ineffective (the x-forwarded-* headers are appended anyway)