No need to save your files from Slack, use Zapier to automatically upload them on OneDrive !
No need to do anything, it will be triggered by your app, and allow you to save time !
You'll just have to chose a trigger and an action, and connect to your accounts.
Zapier provide a privacy of your data. See here
You can find it on https://zapier.com/ and create an account. When you're logged in, choose "Make a Zap" on the dashboard.
On the website, choose "Slack" as the app for the trigger. Then choose "New file" as the trigger event. And finally log in with your slack account.
Add an action, and choose "OneDrive" as the app, and "Upload file" as the event.
That's all, easy right ? Now you can do it for any app. You can look for some ideas here
Nope! Zapier makes it easy for you to move data between your apps without being a developer. We may need you to locate information for certain accounts, but we’ll guide you through any additional steps required and our support champions are here to help you by email should you need assistance.
Trusted by millions across the globe to securely sync data across a variety of web services and get work done. Zapier has globally distributed SRE and security teams on-call 24/7. We constantly monitor security notifications around all 3rd party software libraries and if identified, we immediately apply any relevant security patches as soon as they are released. Our engineers work together with the product teams to ensure that all of Zapier’s code and infrastructure is secure.