I've made an app that makes it possible to schedule a post in Lemmy at an arbitrary time. It's available at https://schedule.lemmings.world and can be used by people from any instance.
I don't store your password if that's what you're asking! I'm planning to make it open source once I make sure I didn't accidentally leave any production secrets in the code.
Anyway, here's how it works:
You log in using your account, the site checks whether it's a valid account using api and if it is, it creates a JWT token that's used to authenticate you against Lemmy. At this point your password is already forgotten and the site has no way of getting it.
The JWT token is effectively the same as having your password - it allows you to do the same things you could if you have logged in normally.
The JWT token is not stored on the server, it's only in a cookie in your browser.
When you schedule a post, the post details, your instance, your username and your JWT token are stored in a job that gets scheduled to run later. This is the only part where any sensitive information (JWT) about you are stored somewhere else than your computer.
After the scheduled job is triggered, it authenticates as you and creates the post as if it were you, immediately afterwards the job config is deleted, meaning the JWT is no longer stored.
The JWT is stored in every scheduled post you make, meaning as long as you have any scheduled post, the JWT is stored somewhere. When all scheduled posts are posted, your JWT is no longer present anywhere on the backend.
Note that due to current technical limitations, even if you cancel a scheduled job, its config (including the JWT) is stored until the original scheduled time. This will be (probably) fixed in future versions when I have some time to work on it.
Hope it clarifies it, let me know if you don't understand any part of it!
I used it for example to post this very post at a time when people from US are most likely to engage (though I'm not sure if the Lemmy demographics is predominantly US, but my gut feeling is it is).
I suppose the only thing is that you wouldn't be able to upload an image to the instance as part of a post - you'd have to upload it somewhere else first, to then be able to refer to it.
For the detractors, register a throwaway account at some random instance, and use that if you want to test it out.
If you're able to properly pore through the source to check it's not stealing anything, then you're capable of scheduling your own posts. The Lemmy API is very simple, it's not rocket science.
I suppose the only thing is that you wouldn’t be able to upload an image to the instance as part of a post
It would be possible but it would add more complexity, more costs etc. I'll probably tackle the problem when I have time, but now I'm glad that I have a version that I can use working.
If you’re able to properly pore through the source to check
I even pointed out some interesting parts regarding this in the README.
Self-hosting is possible, though I don't have a direct support for that right now, you would have to figure it out yourself (it's not hard if you know how to work with the Symfony framework).
Awesome! I'm just starting my workday now, but I could take a look to see if I could put it in a docker container if you would like. I would have to do it after work, which means I probably won't make significant progress until the weekend.
On the todo list, not very urgent, though. Currently you can upload the image somewhere that allows direct link grabbing and put the direct link into the URL field. I use imgur for that.