Gradebook

I'm developing an external system that grades students' work and I'm trying to integrate it with Moodle.

Is there an established way (web service?) that allows external software to import grades into Moodle's gradebook without user interaction? If not, is anyone aware of any plugins for this feature?

As far as I understand, LTI can't be used because it requires a launch request that requires user action in Moodle.

There was a question about this exact thing in 2008 (https://moodle.org/mod/forum/discuss.php?d=92081) and it seems like there wasn't a way back then. Have things changed in the last 11 years?