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digest.go
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digest.go
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package rets
import (
"crypto/md5"
"encoding/hex"
"errors"
"fmt"
"hash"
"io"
"strconv"
"strings"
"sync"
"time"
)
// Digest http://en.wikipedia.org/wiki/Digest_access_authentication
type Digest struct {
Realm string
Nonce string
Algorithm string
Opaque string
Qop string
NonceCount int
m *sync.Mutex
}
func parseChallenge(chall string) (*Digest, error) {
chall = strings.Trim(chall, " \r\n")
if !strings.HasPrefix(strings.ToLower(chall), "digest ") {
return nil, errors.New("Invalid challenge. Challenge must begin with \"digest\"")
}
chall = strings.Trim(chall[7:], " \r\n")
digest, err := parseDirectives(chall, &Digest{Algorithm: "MD5", NonceCount: 1})
if err != nil {
return nil, err
}
return digest, nil
}
func parseDirectives(directives string, d *Digest) (*Digest, error) {
for _, e := range strings.Split(directives, ",") {
directive := strings.SplitN(strings.Trim(e, " \r\n"), "=", 2)
if len(directive) < 2 {
return nil, errors.New("Invalid challenge")
}
switch directive[0] {
case "algorithm":
d.Algorithm = strings.Trim(directive[1], "\"")
case "domain":
break
case "qop":
d.Qop = strings.Trim(directive[1], "\"")
if d.Qop == strings.ToLower("auth-int") {
return nil, errors.New("auth-int is not supported")
}
case "nonce":
d.Nonce = strings.Trim(directive[1], "\"")
case "opaque":
d.Opaque = strings.Trim(directive[1], "\"")
case "realm":
d.Realm = strings.Trim(directive[1], "\"")
case "stale":
break
default:
return nil, errors.New("Invalid challenge. Cannot parse directives.")
}
}
return d, nil
}
// NewDigest ...
func NewDigest(chall string) (*Digest, error) {
c, err := parseChallenge(chall)
if err != nil {
return nil, err
}
return &Digest{
Realm: c.Realm,
Nonce: c.Nonce,
Algorithm: c.Algorithm,
Opaque: c.Opaque,
Qop: c.Qop,
NonceCount: 1,
m: &sync.Mutex{},
}, nil
}
func (d *Digest) createCnonce() string {
asString := strconv.FormatInt(time.Now().Unix(), 10)
return md5ThenHex(md5.New(), asString)
}
func (d *Digest) createHa1(username, password, cnonce string, hasher hash.Hash) string {
//Assuming MD5 or unspecified
a1 := strings.Join([]string{username, d.Realm, password}, ":")
ha1 := md5ThenHex(hasher, a1)
if "md5-sess" == strings.ToLower(d.Algorithm) {
md5sess := strings.Join([]string{ha1, d.Nonce, cnonce}, ":")
ha1 = md5ThenHex(hasher, md5sess)
}
return ha1
}
func (d *Digest) createHa2(method, uri string, hasher hash.Hash) string {
//Assuming qop is auth or unspecified
a2 := method + ":" + uri
return md5ThenHex(hasher, a2)
}
func (d *Digest) createResponse(ha1, ha2, nc, cnonce string, hasher hash.Hash) string {
//qop is unspecified
response := strings.Join([]string{ha1, d.Nonce, ha2}, ":")
//qop is auth
if "auth" == strings.ToLower(d.Qop) {
response = strings.Join([]string{ha1, d.Nonce, nc, cnonce, d.Qop, ha2}, ":")
}
return md5ThenHex(hasher, response)
}
func (d *Digest) computeAuthorization(username, password, method, uri, cnonce string) string {
d.m.Lock()
nc := fmt.Sprintf("%08x", d.NonceCount)
d.NonceCount++
d.m.Unlock()
ha1 := d.createHa1(username, password, cnonce, md5.New())
ha2 := d.createHa2(method, uri, md5.New())
response := d.createResponse(ha1, ha2, nc, cnonce, md5.New())
sl := []string{fmt.Sprintf(`username="%s"`, username)}
sl = append(sl, fmt.Sprintf(`realm="%s"`, d.Realm))
sl = append(sl, fmt.Sprintf(`nonce="%s"`, d.Nonce))
sl = append(sl, fmt.Sprintf(`uri="%s"`, uri))
sl = append(sl, fmt.Sprintf(`response="%s"`, response))
if d.Qop != "" {
sl = append(sl, fmt.Sprintf("qop=%s", d.Qop))
sl = append(sl, fmt.Sprintf("nc=%s", nc))
sl = append(sl, fmt.Sprintf(`cnonce="%s"`, cnonce))
}
if d.Algorithm != "" {
sl = append(sl, fmt.Sprintf(`algorithm="%s"`, d.Algorithm))
}
if d.Opaque != "" {
sl = append(sl, fmt.Sprintf(`opaque="%s"`, d.Opaque))
}
return fmt.Sprintf("Digest %s", strings.Join(sl, ", "))
}
// CreateDigestResponse ...
func (d *Digest) CreateDigestResponse(username, password, method, uri string) string {
return d.computeAuthorization(username, password, method, uri, d.createCnonce())
}
func md5ThenHex(hasher hash.Hash, value string) string {
hasher.Reset()
io.WriteString(hasher, value)
return hex.EncodeToString(hasher.Sum(nil))
}