Weather.
Foreca API is a free Weather API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
Documentation for the Foreca Weather API: REST endpoints for global forecasts, observations, maps and warnings, with live examples and an OpenAPI spec.
Details from developer.foreca.com.

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Weather
The Foreca API is provided by Foreca Developer Portal (developer.foreca.com). Documentation for the Foreca Weather API: REST endpoints for global forecasts, observations, maps and warnings, with live examples and an OpenAPI spec.
Yes. The Foreca API is listed in the Weather 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 Foreca API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the Foreca API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Foreca API is served over HTTPS, so it's safe to use in production.