Classic: setting (and uploading) a user avatar through the API

Hey folks,

The docs aren't very clear on how to actually upload a user avatar on Classic. I think I have to upload an image to an album and then link to that image from the userprofile endpoint, but the steps are unclear. Which album? How do I tell it which album?

The reason: I have a whole bunch of old migrated avatars that are http endpoints. Many of the users with those avatars were very active but are no longer with us. Our SEO team says we should update them to https to eliminate mixed http/https. Seems like an easy one-off script, but I don't see the right set of incantations. 

Any pointers? I'll be doing this in python with an AI copilot if that helps (I'm a rusty developer).

Thanks!