ocsp: add Response.Raw

Fixes golang/go#38340

Change-Id: I77afc901584ac3361eafa13c9ee9f8cf9ec2ee28
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/389256
Trust: Roland Shoemaker <roland@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

ocsp.go

@@ -345,6 +345,8 @@ func (req *Request) Marshal() ([]byte, error) {
 // Response represents an OCSP response containing a single SingleResponse. See
 // RFC 6960.
 type Response struct {
+	Raw []byte
+
 	// Status is one of {Good, Revoked, Unknown}
 	Status                                        int
 	SerialNumber                                  *big.Int
@@ -518,6 +520,7 @@ func ParseResponseForCert(bytes []byte, cert, issuer *x509.Certificate) (*Respon
 	}
 
 	ret := &Response{
+		Raw:                bytes,
 		TBSResponseData:    basicResp.TBSResponseData.Raw,
 		Signature:          basicResp.Signature.RightAlign(),
 		SignatureAlgorithm: getSignatureAlgorithmFromOID(basicResp.SignatureAlgorithm.Algorithm),