We've done various integrations with Totara report builder, custom plugins and recently with report_customsql to allow an export of these types of reports using a web service token.

It would be awesome if we could do the same with report builder.

So proposing to remove this endpoint

/reportbuilder/download.php?download=csv&id=4

and instead convert it to a normal plugin file url

/pluginfile.php/1/core_reportbuilder/download?format=csv&id=4&foo=bar&foo2=bar2

The UI would not change it would just go to the new url and mostly it's all just moving code around with no functional change.

Then we now have the option for free of allowing an arbitrary report via web services:

/webservice/pluginfile.php/1/core_reportbuilder/download?format=csv&id=4&foo=bar&foo2=bar2&token=MYWEBSERVICETOKEN

If the report has any filters then these can also be tacked onto the url as extra query params, eg foo=bar above.