
Line Login, Share on Line, Social Plugins and more.
Line API is a free Social API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
Details from developers.line.biz.

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The Line API is provided by LINE Developers (developers.line.biz).
Yes. The Line API is listed in the Social 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 Line API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the Line API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Line API is served over HTTPS, so it's safe to use in production.