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OpenAPIHub API is a free Development API that requires X-Mashape-Key authentication, is served over HTTPS and has unconfirmed CORS support.
Details from hub.openapihub.com.

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The OpenAPIHub API is provided by OpenAPIHub Marketplace (hub.openapihub.com).
Yes. The OpenAPIHub API is listed in the Development 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 OpenAPIHub API uses X-Mashape-Key authentication, so you need to register for credentials before making requests.
CORS support for the OpenAPIHub API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The OpenAPIHub API is served over HTTPS, so it's safe to use in production.