Retrieve programmatically SharePoint Online system page html content

How can I get HTML content of a SharePoint online page from code, e.g. PowerShell?

Invoke-WebRequest returns “Sign in to your account” page, not a real page, even with -Token option.

Thanks to Denis Molodtsov, the solution is found. It turns out the “Invoke-PnPSPRestMethod” PnP cmdlet works not only against /api endpoints, but also against site pages and system pages.

But (as per my experience) it works only with PnP.PowerShell and with -UseWebLogin authentication option and with -raw parameter.

Connect-PnPOnline -url $siteUrl -UseWebLogin
Invoke-PnPSPRestMethod -url /_layouts/15/viewlsts.aspx -Raw

Other combination of authentication options ( -interactive, -clientId, -Token, -SPOManagementShell, -PnPManagementShell ) – worked well, but only for /_api endpoints, and gave me “401 UNAUTHORIZED” against system/site pages.
Unattended authentication (with clientId, clientSecret and certificate) – same.

Legacy PnP module SharePointPnPPowerShellOnline did not work at all: “EXCEPTION,PnP.PowerShell.Commands.Admin.InvokeSPRestMethod”.

I tested it with
– SharePointPnPPowerShellOnline v 3.29.2101.0 (under Windows PowerShell 5.1) and
– PnP.PowerShell 1.8.0. (both Windows PowerShell 5.1 and .net core PowerShell 7.1.5)