A few words about Fluyt. Why not wget or something similar? That doesn't work when the web-app dynamically builds its DOM with JS!
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So, I use WPEWebKit, with an headless backend and a web-extension that fakes a user interaction (scroll) and waits a second before dumping the HTML body to the stdout.
Why NIH PhantomJS? Well PhantomJS is un-maintained, likely plagued with security bugs, and Qt based anyway, which I don't want on my server. WPE is a perfect fit for this project.
A Flatpak repo is provided for convenience. Tested on a Debian Stretch box (x86_64) with Flatpak 1.2 from stretch-backports. Works like a charm!