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// 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)
}
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