EOxC connects to OpenSearch and WMS services which in the above link are provided by Sentinel Hub. Downloads are provided via the sentinel-s2-l1c bucket and the landsat-pds bucket on Amazon Simple Storage Service (S3).
Support has been generously provided by the European Space Agency (ESA).
Technical details on how to use the client and supported features are provided in an earlier blog post. We might need to eventually write a new post to detail the functionality added since March last year.
Contributions and feedback are always welcome on GitHub!