Can't get ffmpeg to use headers passed to it

I am trying to play some media with inputstream.ffmpegdirect on Kodi 21.1 on MACOS

I need to pass some headers as well as the stream info to get the URL
headers = {
"X-Plex-Token" : token,
"X-Forwarded-For" : "173.166.164.121",
"user-agent" : "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36 Edg/131.0.0.0"

    }

The stream URL looks like https://epg.provider.plex.tv/library/parts/5e20b730f2f8d5003d739db7-646fab0e43d6d6838db81a6a?X-Plex-Token=nHD9WHxxk3uwKwL7VWhG

I am adding the headers to the URL with this bit of python
x = ""
for key in headers:
x += u'{0}={1}&'.format(key, urllib.parse.quote(u'{}'.format(headers[key]).encode('utf8')))

And then putting it all together
liz = xbmcgui.ListItem(path=url + '|' + x)
liz.setProperty('inputstream', 'inputstream.ffmpegdirect')
liz.setProperty('IsPlayable', 'true')
liz.setProperty('inputstream.ffmpegdirect.stream_mode', 'timeshift')
liz.setProperty('inputstream.ffmpegdirect.is_realtime_stream', 'true')
liz.setProperty('inputstream.ffmpegdirect.manifest_type', 'hls')
xbmcplugin.setResolvedUrl(handle, True, liz)

    looking at the log, it seems the initial curl works
    CCurlFile::GetMimeType - <https://epg.provider.plex.tv/library/parts/5e20b730f2f8d5003d739db7-646fab0e43d6d6838db81a6a?X-Plex-Token=nHD9WHxxk3uwKwL7VWhG|X-Plex-Token=nHD9WHxxk3uwKwL7VWhG&X-Forwarded-For=173.166.164.121&user-agent=Mozilla/5.0%20%28Macintosh%3B%20Intel%20Mac%20OS%20X%2010_15_7%29%20AppleWebKit/537.36%20%28KHTML%2C%20like%20Gecko%29%20Chrome/131.0.0.0%20Safari/537.36%20Edg/131.0.0.0&> -> application/x-mpegurl
    
    But, the headers are ignored / changed later on

2025-01-07 16:03:30.260 T:332467 debug : AddOnLog: inputstream.ffmpegdirect: CDVDDemuxFFmpeg::GetFFMpegOptionsFromInput() adding ffmpeg option 'user_agent: 0'
2025-01-07 16:03:30.260 T:332467 debug : AddOnLog: inputstream.ffmpegdirect: CDVDDemuxFFmpeg::GetFFMpegOptionsFromInput() adding custom header option 'X-Forwarded-For: 0'
2025-01-07 16:03:30.260 T:332467 debug : AddOnLog: inputstream.ffmpegdirect: CDVDDemuxFFmpeg::GetFFMpegOptionsFromInput() ignoring header option 'X-Plex-Token'
2025-01-07 16:03:30.260 T:332467 debug : AddOnLog: inputstream.ffmpegdirect: CDVDDemuxFFmpeg::GetFFMpegOptionsFromInput() adding ffmpeg option 'user_agent: 0'

i have attached the full log file
kodi.log.txt

any pointers/help would be greatly appreciated!

Start at CDVDDemuxFFmpeg::GetFFMpegOptionsFromInput(), the entry point named in the log, and trace how URL options become FFmpeg options or custom headers. Reproduce the reported Kodi 21.1 inputstream.ffmpegdirect case with the supplied URL and headers; done means the intended headers are preserved and passed through instead of being ignored or changed.