vendor: add cfssl dependency

vendor/github.com/cloudflare/cfssl/auth/auth.go

@@ -0,0 +1,94 @@
+// Package auth implements an interface for providing CFSSL
+// authentication. This is meant to authenticate a client CFSSL to a
+// remote CFSSL in order to prevent unauthorised use of the signature
+// capabilities. This package provides both the interface and a
+// standard HMAC-based implementation.
+package auth
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+)
+
+// An AuthenticatedRequest contains a request and authentication
+// token. The Provider may determine whether to validate the timestamp
+// and remote address.
+type AuthenticatedRequest struct {
+	// An Authenticator decides whether to use this field.
+	Timestamp     int64  `json:"timestamp,omitempty"`
+	RemoteAddress []byte `json:"remote_address,omitempty"`
+	Token         []byte `json:"token"`
+	Request       []byte `json:"request"`
+}
+
+// A Provider can generate tokens from a request and verify a
+// request. The handling of additional authentication data (such as
+// the IP address) is handled by the concrete type, as is any
+// serialisation and state-keeping.
+type Provider interface {
+	Token(req []byte) (token []byte, err error)
+	Verify(aReq *AuthenticatedRequest) bool
+}
+
+// Standard implements an HMAC-SHA-256 authentication provider. It may
+// be supplied additional data at creation time that will be used as
+// request || additional-data with the HMAC.
+type Standard struct {
+	key []byte
+	ad  []byte
+}
+
+// New generates a new standard authentication provider from the key
+// and additional data. The additional data will be used when
+// generating a new token.
+func New(key string, ad []byte) (*Standard, error) {
+	if splitKey := strings.SplitN(key, ":", 2); len(splitKey) == 2 {
+		switch splitKey[0] {
+		case "env":
+			key = os.Getenv(splitKey[1])
+		case "file":
+			data, err := ioutil.ReadFile(splitKey[1])
+			if err != nil {
+				return nil, err
+			}
+			key = string(data)
+		default:
+			return nil, fmt.Errorf("unknown key prefix: %s", splitKey[0])
+		}
+	}
+
+	keyBytes, err := hex.DecodeString(key)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Standard{keyBytes, ad}, nil
+}
+
+// Token generates a new authentication token from the request.
+func (p Standard) Token(req []byte) (token []byte, err error) {
+	h := hmac.New(sha256.New, p.key)
+	h.Write(req)
+	h.Write(p.ad)
+	return h.Sum(nil), nil
+}
+
+// Verify determines whether an authenticated request is valid.
+func (p Standard) Verify(ad *AuthenticatedRequest) bool {
+	if ad == nil {
+		return false
+	}
+
+	// Standard token generation returns no error.
+	token, _ := p.Token(ad.Request)
+	if len(ad.Token) != len(token) {
+		return false
+	}
+
+	return hmac.Equal(token, ad.Token)
+}