add Digest authentication for http proxy server

https://datatracker.ietf.org/doc/html/rfc2617
server will send both Basic and Digest header to client
client can use either Basic or Digest for authentication

Change-Id: Iaa6629c143551770c836af3ead823bd148b244c6

common/auth/auth.go

@@ -1,6 +1,23 @@
 package auth
 
-import "github.com/sagernet/sing/common"
+import (
+	"crypto/md5"
+	"encoding/hex"
+	"fmt"
+
+	"github.com/sagernet/sing/common"
+	"github.com/sagernet/sing/common/param"
+)
+
+const Realm = "sing-box"
+
+type Challenge struct {
+        Username  string
+        Nonce     string
+        CNonce    string
+        Nc        string
+        Response  string
+}
 
 type User struct {
 	Username string
@@ -28,3 +45,55 @@ func (au *Authenticator) Verify(username string, password string) bool {
 	passwordList, ok := au.userMap[username]
 	return ok && common.Contains(passwordList, password)
 }
+
+func (au *Authenticator) VerifyDigest(method string, uri string, s string) (string, bool) {
+	c, err := ParseChallenge(s)
+	if err != nil {
+		return "", false
+	}
+	if c.Username == "" || c.Nonce == "" || c.Nc == "" || c.CNonce == "" || c.Response == "" {
+		return "", false
+	}
+	passwordList, ok := au.userMap[c.Username]
+	if ok {
+		for _, password := range passwordList {
+			ha1 := md5str(c.Username + ":" + Realm + ":" + password)
+			ha2 := md5str(method + ":" + uri)
+			resp := md5str(ha1 + ":" + c.Nonce + ":" + c.Nc + ":" + c.CNonce + ":auth:" + ha2)
+			if resp == c.Response {
+				return c.Username, true
+			}
+		}
+	}
+	return "", false
+}
+
+func ParseChallenge(s string) (*Challenge, error) {
+	pp, err := param.Parse(s)
+	if err != nil {
+		return nil, fmt.Errorf("digest: invalid challenge: %w", err)
+	}
+	var c Challenge
+
+	for _, p := range pp {
+		switch p.Key {
+		case "username":
+			c.Username = p.Value
+		case "nonce":
+			c.Nonce = p.Value
+		case "cnonce":
+			c.CNonce = p.Value
+		case "nc":
+			c.Nc = p.Value
+		case "response":
+			c.Response = p.Value
+		}
+	}
+	return &c, nil
+}
+
+func md5str(str string) string  {
+	h := md5.New()
+	h.Write([]byte(str))
+	return hex.EncodeToString(h.Sum(nil))
+}

common/param/param.go

@@ -0,0 +1,189 @@
+package param
+
+// code retrieve from https://github.com/icholy/digest/tree/master/internal/param
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// Param is a key/value header parameter
+type Param struct {
+	Key   string
+	Value string
+	Quote bool
+}
+
+// String returns the formatted parameter
+func (p Param) String() string {
+	if p.Quote {
+		return p.Key + "=" + strconv.Quote(p.Value)
+	}
+	return p.Key + "=" + p.Value
+}
+
+// Format formats the parameters to be included in the header
+func Format(pp ...Param) string {
+	var b strings.Builder
+	for i, p := range pp {
+		if i > 0 {
+			b.WriteString(", ")
+		}
+		b.WriteString(p.String())
+	}
+	return b.String()
+}
+
+// Parse parses the header parameters
+func Parse(s string) ([]Param, error) {
+	var pp []Param
+	br := bufio.NewReader(strings.NewReader(s))
+	for i := 0; true; i++ {
+		// skip whitespace
+		if err := skipWhite(br); err != nil {
+			return nil, err
+		}
+		// see if there's more to read
+		if _, err := br.Peek(1); err == io.EOF {
+			break
+		}
+		// read key/value pair
+		p, err := parseParam(br, i == 0)
+		if err != nil {
+			return nil, fmt.Errorf("param: %w", err)
+		}
+		pp = append(pp, p)
+	}
+	return pp, nil
+}
+
+func parseIdent(br *bufio.Reader) (string, error) {
+	var ident []byte
+	for {
+		b, err := br.ReadByte()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return "", err
+		}
+		if !(('a' <= b && b <= 'z') || ('A' <= b && b <= 'Z') || '0' <= b && b <= '9' || b == '-') {
+			if err := br.UnreadByte(); err != nil {
+				return "", err
+			}
+			break
+		}
+		ident = append(ident, b)
+	}
+	return string(ident), nil
+}
+
+func parseByte(br *bufio.Reader, expect byte) error {
+	b, err := br.ReadByte()
+	if err != nil {
+		if err == io.EOF {
+			return fmt.Errorf("expected '%c', got EOF", expect)
+		}
+		return err
+	}
+	if b != expect {
+		return fmt.Errorf("expected '%c', got '%c'", expect, b)
+	}
+	return nil
+}
+
+func parseString(br *bufio.Reader) (string, error) {
+	var s []rune
+	// read the open quote
+	if err := parseByte(br, '"'); err != nil {
+		return "", err
+	}
+	// read the string
+	var escaped bool
+	for {
+		r, _, err := br.ReadRune()
+		if err != nil {
+			return "", err
+		}
+		if escaped {
+			s = append(s, r)
+			escaped = false
+			continue
+		}
+		if r == '\\' {
+			escaped = true
+			continue
+		}
+		// closing quote
+		if r == '"' {
+			break
+		}
+		s = append(s, r)
+	}
+	return string(s), nil
+}
+
+func skipWhite(br *bufio.Reader) error {
+	for {
+		b, err := br.ReadByte()
+		if err != nil {
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+		if b != ' ' {
+			return br.UnreadByte()
+		}
+	}
+}
+
+func parseParam(br *bufio.Reader, first bool) (Param, error) {
+	// skip whitespace
+	if err := skipWhite(br); err != nil {
+		return Param{}, err
+	}
+	if !first {
+		// read the comma separator
+		if err := parseByte(br, ','); err != nil {
+			return Param{}, err
+		}
+		// skip whitespace
+		if err := skipWhite(br); err != nil {
+			return Param{}, err
+		}
+	}
+	// read the key
+	key, err := parseIdent(br)
+	if err != nil {
+		return Param{}, err
+	}
+	// skip whitespace
+	if err := skipWhite(br); err != nil {
+		return Param{}, err
+	}
+	// read the equals sign
+	if err := parseByte(br, '='); err != nil {
+		return Param{}, err
+	}
+	// skip whitespace
+	if err := skipWhite(br); err != nil {
+		return Param{}, err
+	}
+	// read the value
+	var value string
+	var quote bool
+	if b, _ := br.Peek(1); len(b) == 1 && b[0] == '"' {
+		quote = true
+		value, err = parseString(br)
+	} else {
+		value, err = parseIdent(br)
+	}
+	if err != nil {
+		return Param{}, err
+	}
+	return Param{Key: key, Value: value, Quote: quote}, nil
+}

protocol/http/handshake.go

@@ -3,7 +3,9 @@ package http
 import (
 	std_bufio "bufio"
 	"context"
+	"crypto/rand"
 	"encoding/base64"
+	"encoding/hex"
 	"io"
 	"net"
 	"net/http"
@@ -42,6 +44,12 @@ func HandleConnectionEx(
 				authOk   bool
 			)
 			authorization := request.Header.Get("Proxy-Authorization")
+			if strings.HasPrefix(authorization, "Digest ") {
+				username, authOk = authenticator.VerifyDigest(request.Method, request.RequestURI, authorization[7:])
+				if authOk {
+					ctx = auth.ContextWithUser(ctx, username)
+				}
+			}
 			if strings.HasPrefix(authorization, "Basic ") {
 				userPassword, _ := base64.URLEncoding.DecodeString(authorization[6:])
 				userPswdArr := strings.SplitN(string(userPassword), ":", 2)
@@ -56,10 +64,31 @@ func HandleConnectionEx(
 			}
 			if !authOk {
 				// Since no one else is using the library, use a fixed realm until rewritten
-				err = responseWith(
-					request, http.StatusProxyAuthRequired,
-					"Proxy-Authenticate", `Basic realm="sing-box" charset="UTF-8"`,
-				).Write(conn)
+				// define realm in common/auth package, still "sing-box" now
+				nonce := "";
+				randomBytes := make([]byte, 16)
+				_, err = rand.Read(randomBytes)
+				if err == nil {
+					nonce = hex.EncodeToString(randomBytes)
+				}
+				if nonce == "" {
+					err = responseWithBody(
+						request, http.StatusProxyAuthRequired,
+						"Proxy authentication required",
+						"Content-Type", "text/plain; charset=utf-8",
+						"Proxy-Authenticate", "Basic realm=\"" + auth.Realm + "\"",
+						"Connection", "close",
+					).Write(conn)
+				} else {
+					err = responseWithBody(
+						request, http.StatusProxyAuthRequired,
+						"Proxy authentication required",
+						"Content-Type", "text/plain; charset=utf-8",
+						"Proxy-Authenticate", "Basic realm=\"" + auth.Realm + "\"",
+						"Proxy-Authenticate", "Digest realm=\"" + auth.Realm + "\", nonce=\"" + nonce + "\", qop=\"auth\", stale=false",
+						"Connection", "close",
+					).Write(conn)
+				}
 				if err != nil {
 					return err
 				}
@@ -68,7 +97,8 @@ func HandleConnectionEx(
 				} else if authorization != "" {
 					return E.New("http: authentication failed, Proxy-Authorization=", authorization)
 				} else {
-					return E.New("http: authentication failed, no Proxy-Authorization header")
+					//return E.New("http: authentication failed, no Proxy-Authorization header")
+					continue
 				}
 			}
 		}
@@ -270,3 +300,31 @@ func responseWith(request *http.Request, statusCode int, headers ...string) *htt
 		Header:     header,
 	}
 }
+
+func responseWithBody(request *http.Request, statusCode int, body string, headers ...string) *http.Response {
+	var header http.Header
+	if len(headers) > 0 {
+		header = make(http.Header)
+		for i := 0; i < len(headers); i += 2 {
+			header.Add(headers[i], headers[i+1])
+		}
+	}
+	var bodyReadCloser io.ReadCloser
+	var bodyContentLength = int64(0)
+	if body != "" {
+		bodyReadCloser = io.NopCloser(strings.NewReader(body))
+		bodyContentLength = int64(len(body))
+	}
+	return &http.Response{
+		StatusCode:    statusCode,
+		Status:        http.StatusText(statusCode),
+		Proto:         request.Proto,
+		ProtoMajor:    request.ProtoMajor,
+		ProtoMinor:    request.ProtoMinor,
+		Header:        header,
+		Body:          bodyReadCloser,
+		ContentLength: bodyContentLength,
+		Close:         true,
+        }
+}
+