1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
|
package main
import (
"crypto/hmac"
"crypto/rand"
"crypto/sha256"
"crypto/subtle"
"encoding/base64"
"encoding/binary"
"errors"
"flag"
"log"
"net/http"
"net/http/httputil"
"net/url"
"strings"
"time"
"unsafe"
)
var (
difficulty uint
listenAddr string
destHost string
secondary bool
)
func init() {
flag.UintVar(&difficulty, "difficulty", 17, "leading zero bits required for the challenge")
flag.StringVar(&listenAddr, "listen", ":8081", "address to listen on")
flag.StringVar(&destHost, "upstream", "http://127.0.0.1:8080", "destination url base to proxy to")
flag.BoolVar(&secondary, "secondary", false, "trust X-Forwarded-For headers")
flag.Parse()
}
var (
privkey = make([]byte, 32)
privkeyHash = make([]byte, 0, sha256.Size)
)
func init() {
if _, err := rand.Read(privkey); err != nil {
log.Fatal(err)
}
h := sha256.New()
h.Write(privkey)
privkeyHash = h.Sum(nil)
}
var reverseProxy *httputil.ReverseProxy
func init() {
parsedURL, err := url.Parse(destHost)
if err != nil {
log.Fatal(err)
}
reverseProxy = httputil.NewSingleHostReverseProxy(parsedURL)
}
type tparams struct {
UnsignedTokenBase64 string
NeedBits uint
Message string
}
func main() {
log.Fatal(http.ListenAndServe(listenAddr, http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
log.Println(getRemoteIP(request), request.RequestURI, request.Header.Get("User-Agent"))
cookie, err := request.Cookie("powxy")
if err != nil {
if !errors.Is(err, http.ErrNoCookie) {
http.Error(writer, "error fetching cookie", http.StatusInternalServerError)
return
}
}
expectedToken := makeSignedToken(request)
if validateCookie(cookie, expectedToken) {
proxyRequest(writer, request)
return
}
authPage := func(message string) {
_ = tmpl.Execute(writer, tparams{
UnsignedTokenBase64: base64.StdEncoding.EncodeToString(expectedToken[:sha256.Size]),
Message: message,
NeedBits: difficulty,
})
}
if request.ParseForm() != nil {
authPage("You submitted a malformed form.")
return
}
formValues, ok := request.PostForm["powxy"]
if !ok {
authPage("")
return
} else if len(formValues) != 1 {
authPage("You submitted an invalid number of form values.")
return
}
nonce, err := base64.StdEncoding.DecodeString(formValues[0])
if err != nil {
authPage("Your submission was improperly encoded.")
return
}
if len(nonce) > 32 {
authPage("Your submission was too long.")
return
}
h := sha256.New()
h.Write(expectedToken[:sha256.Size])
h.Write(nonce)
ck := h.Sum(nil)
if !validateBitZeros(ck, difficulty) {
authPage("Your submission was incorrect, or your session has expired while submitting.")
return
}
http.SetCookie(writer, &http.Cookie{
Name: "powxy",
Value: base64.StdEncoding.EncodeToString(expectedToken),
})
http.Redirect(writer, request, "", http.StatusSeeOther)
})))
}
func validateCookie(cookie *http.Cookie, expectedToken []byte) bool {
if cookie == nil {
return false
}
gotToken, err := base64.StdEncoding.DecodeString(cookie.Value)
if err != nil {
return false
}
return subtle.ConstantTimeCompare(gotToken, expectedToken) == 1
}
func getRemoteIP(request *http.Request) (remoteIP string) {
if secondary {
remoteIP, _, _ = strings.Cut(request.Header.Get("X-Forwarded-For"), ",")
}
if remoteIP == "" {
remoteIP = request.RemoteAddr
index := strings.LastIndex(remoteIP, ":")
if index != -1 {
remoteIP = remoteIP[:index]
}
}
return
}
func makeSignedToken(request *http.Request) []byte {
buf := make([]byte, 0, 2*sha256.Size)
timeBuf := make([]byte, binary.MaxVarintLen64)
binary.PutVarint(timeBuf, time.Now().Unix()/604800)
remoteIP := getRemoteIP(request)
h := sha256.New()
h.Write(timeBuf)
h.Write(stringToBytes(remoteIP))
h.Write(stringToBytes(request.Header.Get("User-Agent")))
h.Write(stringToBytes(request.Header.Get("Accept-Encoding")))
h.Write(stringToBytes(request.Header.Get("Accept-Language")))
h.Write(privkeyHash)
buf = h.Sum(buf)
if len(buf) != sha256.Size {
panic("unexpected buffer length after hashing contents")
}
mac := hmac.New(sha256.New, privkey)
mac.Write(buf)
buf = mac.Sum(buf)
if len(buf) != 2*sha256.Size {
panic("unexpected buffer length after hmac")
}
return buf
}
func proxyRequest(writer http.ResponseWriter, request *http.Request) {
reverseProxy.ServeHTTP(writer, request)
}
func stringToBytes(s string) (bytes []byte) {
return unsafe.Slice(unsafe.StringData(s), len(s))
}
|
