Some private keys not supported

[tyuen]

When calling sign, an exception was thrown about atob being called with invalid text.

After debugging, I narrowed it down to the pemToArrayBuffer call and it turns out my private key didn't begin with:
"-----BEGIN PRIVATE KEY-----"
but began with
"-----BEGIN RSA PRIVATE KEY-----"

I was able to resolve this by converting the private key to the correct format with:

openssl pkcs8 -topk8 -nocrypt -in private.pem -out private2.pem

Maybe you could put something in the FAQ in case someone encounters this.