This adds support for crypto.Signer-based RSA and ECDSA private keys.
This enables using opaque signing keys as explained in the documentation
for crypto.Signer.
The support is in the form of a new NewSignerPrivateKey function which
makes a PrivateKey from a crypto.Signer.
Fixesgolang/go#15841.
Change-Id: Ice2ec2793a9f5409a5bfd4e5e49d919e14ede1e0
Reviewed-on: https://go-review.googlesource.com/23802
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>