Global solar and weather data for energy and agriculture.
NASA POWER API is a free Weather API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
POWER Documentation Site
Details from power.larc.nasa.gov.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
US coastal tides, water levels, currents and meteorological observations
The NASA POWER API is provided by NASA POWER (power.larc.nasa.gov). POWER Documentation Site
Yes. The NASA POWER 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.
No. The NASA POWER API requires no authentication, so you can start making requests without signing up.
Yes. The NASA POWER API supports CORS, so front-end JavaScript can call it directly.
Yes. The NASA POWER API is served over HTTPS, so it's safe to use in production.