File Sharing and Storage.
OneDrive API is a free Cloud Storage & File Sharing API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
OneDrive is enterprise content storage for all. Find resources to connect to billions of files and add seamless file storage, share and collaborate at scale.
Details from developer.microsoft.com.

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The OneDrive API is provided by Microsoft OneDrive Dev Center (developer.microsoft.com). OneDrive is enterprise content storage for all. Find resources to connect to billions of files and add seamless file storage, share and collaborate at scale.
Yes. The OneDrive API is listed in the Cloud Storage & File Sharing category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The OneDrive API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the OneDrive API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The OneDrive API is served over HTTPS, so it's safe to use in production.