[2.8] openssl_privatekey: forgot to add secp256r1 #58610
Backport of #58605 to stable-2.8.
I'm not sure whether this really counts as a bugfix, or is more a feature request, since this adds a new curve. Since the original intend of elliptic curve support was to cover the most important curves, this one should have really been there in the first place. Mentioning secp256k1 instead of secp256r1 as most interoperable is definitely a bug: secp256r1 and secp384r1 are the only elliptic curves supported by almost all browsers (excluding too old ones), while secp256k1 usually isn't supported. (For example, both Chrome 49 and IE11 only support these two curves, while Firefox 47 and Safari 7 additionally support secp521r1; search for "named groups" in the links for details. Safari 10 still supports no other groups, so even with more modern browsers one still is stuck with these two curves.)