Creating base64 private key

[luveti]

VapidSignatureBuilder::from_base64 says:

Creates a new builder from a raw base64-encoded private key

But doesn't provide an example like the public key documentation does:

openssl ec -in private.pem -pubout -outform DER|tail -c 65|base64|tr '/+' '_-'|tr -d '\n'

Would the following work? I've removed the -pubout argument so that it outputs the private key instead.

openssl ec -in private.pem -outform DER|tail -c 65|base64|tr '/+' '_-'|tr -d '\n'

I'm not sure if the tail needs modified or not; The public key docs don't mention why this tail is needed.

[niklasf]

I think it should be tail -c 32, for the raw bytes of a P-256 key.

If you can confirm, we should probably include it in the documentation.