I've once again tried adding HLSStreams instead of having the plugin yield progressive HTTPStreams (see #4609 (comment)), but to no luck. Server response 403 using the same URL logic as the HTTP "FLV" streams.
The issue from the report in #4684 was stream data sometimes not being base64 encoded, so a different regex and validation logic was needed. Because of this, I rewrote and cleaned up the entire plugin in one go, and also added stream metadata.
$ streamlink -l debug 'https://www.huya.com/688062'
[cli][debug] OS: Linux-5.18.14-1-git-x86_64-with-glibc2.35
[cli][debug] Python: 3.10.5
[cli][debug] Streamlink: 4.2.0+26.gad51118e
[cli][debug] Dependencies:
[cli][debug] isodate: 0.6.1
[cli][debug] lxml: 4.9.0
[cli][debug] pycountry: 22.3.5
[cli][debug] pycryptodome: 3.14.1
[cli][debug] PySocks: 1.7.1
[cli][debug] requests: 2.28.1
[cli][debug] websocket-client: 1.3.2
[cli][debug] Arguments:
[cli][debug] url=https://www.huya.com/688062
[cli][debug] --loglevel=debug
[cli][debug] --player=mpv
[cli][info] Found matching plugin huya for URL https://www.huya.com/688062
[plugins.huya][debug] QUALITY_WEIGHTS: {'source_ws': 100, 'source_al': 0, 'source_tx': -1, 'source_hw': -1, 'source_bd': -1}
Available streams: source_tx (worst), source_hw, source_bd, source_al, source_ws (best)
$ streamlink -l debug 'https://www.huya.com/dongerlol'
[cli][debug] OS: Linux-5.18.14-1-git-x86_64-with-glibc2.35
[cli][debug] Python: 3.10.5
[cli][debug] Streamlink: 4.2.0+26.gad51118e
[cli][debug] Dependencies:
[cli][debug] isodate: 0.6.1
[cli][debug] lxml: 4.9.0
[cli][debug] pycountry: 22.3.5
[cli][debug] pycryptodome: 3.14.1
[cli][debug] PySocks: 1.7.1
[cli][debug] requests: 2.28.1
[cli][debug] websocket-client: 1.3.2
[cli][debug] Arguments:
[cli][debug] url=https://www.huya.com/dongerlol
[cli][debug] --loglevel=debug
[cli][debug] --player=mpv
[cli][info] Found matching plugin huya for URL https://www.huya.com/dongerlol
[plugins.huya][debug] QUALITY_WEIGHTS: {'source_al': 0, 'source_tx': -1, 'source_hw': -1, 'source_bd': 100}
Available streams: source_tx (worst), source_hw, source_al, source_bd (best)