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refactor(backend): extract to pkg/cap
This commit is contained in:
ryan
+259
@@ -0,0 +1,259 @@
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// Copyright 2026 Arctel.net
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// SPDX-License-Identifier: Apache-2.0
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// Package cap 提供人机验证（CAPTCHA）功能
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package cap
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import (
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"crypto/hmac"
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"crypto/rand"
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"crypto/sha256"
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"encoding/base64"
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"encoding/hex"
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"encoding/json"
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"errors"
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"strconv"
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"strings"
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"time"
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)
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const (
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jwtHeaderB64 = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9"
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jwtPartsCount = 3 // JWT 三段结构
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defaultChallengeCount = 50 // 默认 PoW 难题数
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defaultChallengeSize = 32 // 默认盐值长度
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defaultDifficulty = 4 // 默认难度
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defaultNonceLength = 25 // 随机 Nonce 字节长度
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defaultExpires = 10 * time.Minute // 默认过期时间
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)
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// ChallengeConfig holds parameters for the PoW challenge
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type ChallengeConfig struct {
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Count int // Number of puzzles (c)
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Size int // Salt length (s)
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Difficulty int // Difficulty prefix length (d)
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Expires time.Duration // Challenge TTL
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}
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// ChallengeResponse is returned to the client
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type ChallengeResponse struct {
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Challenge struct {
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C int `json:"c"`
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S int `json:"s"`
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D int `json:"d"`
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} `json:"challenge"`
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Token string `json:"token"`
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Expires int64 `json:"expires"` // ms timestamp
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}
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// ChallengePayload represents the signed JWT payload
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type ChallengePayload struct {
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Nonce string `json:"n"`
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Count int `json:"c"`
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Size int `json:"s"`
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Difficulty int `json:"d"`
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Expires int64 `json:"exp"` // ms timestamp
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IssuedAt int64 `json:"iat"` // ms timestamp
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Scope string `json:"sk,omitempty"`
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}
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// RedeemRequest payload sent by client
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type RedeemRequest struct {
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Token string `json:"token"`
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Solutions []int `json:"solutions"`
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}
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// RedeemResponse returned to client after verification
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type RedeemResponse struct {
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Success bool `json:"success"`
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Token string `json:"token,omitempty"`
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Expires int64 `json:"expires,omitempty"`
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Error string `json:"error,omitempty"`
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}
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func b64urlEncode(data []byte) string {
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return base64.RawURLEncoding.EncodeToString(data)
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}
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func b64urlDecode(str string) ([]byte, error) {
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return base64.RawURLEncoding.DecodeString(str)
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}
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// RandomHex generates a cryptographically secure random hexadecimal string of the specified byte length.
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func RandomHex(byteLen int) string {
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bytes := make([]byte, byteLen)
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if _, err := rand.Read(bytes); err != nil {
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panic(err)
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}
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return hex.EncodeToString(bytes)
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}
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func jwtSign(payload []byte, secret []byte) string {
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body := b64urlEncode(payload)
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sigInput := jwtHeaderB64 + "." + body
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mac := hmac.New(sha256.New, secret)
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mac.Write([]byte(sigInput))
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sig := mac.Sum(nil)
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return sigInput + "." + b64urlEncode(sig)
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}
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func jwtVerify(token string, secret []byte) ([]byte, error) {
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parts := strings.Split(token, ".")
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if len(parts) != jwtPartsCount {
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return nil, errors.New(errInvalidTokenFormat)
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}
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if parts[0] != jwtHeaderB64 {
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return nil, errors.New(errInvalidHeader)
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}
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sigInput := parts[0] + "." + parts[1]
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mac := hmac.New(sha256.New, secret)
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mac.Write([]byte(sigInput))
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expectedSig := mac.Sum(nil)
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actualSig, err := b64urlDecode(parts[2])
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if err != nil {
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return nil, err
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}
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if !hmac.Equal(expectedSig, actualSig) {
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return nil, errors.New(errSignatureMismatch)
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}
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payload, err := b64urlDecode(parts[1])
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if err != nil {
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return nil, err
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}
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return payload, nil
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}
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// JwtSigHex extracts the signature part of a JWT token and returns it as a hexadecimal string.
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func JwtSigHex(token string) string {
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parts := strings.Split(token, ".")
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if len(parts) != jwtPartsCount {
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return ""
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}
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sigBytes, err := b64urlDecode(parts[2])
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if err != nil {
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return ""
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}
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return hex.EncodeToString(sigBytes)
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}
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// GenerateChallenge produces a new challenge and signed token
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func GenerateChallenge(secret []byte, conf ChallengeConfig, scope string) (*ChallengeResponse, error) {
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if conf.Count <= 0 {
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conf.Count = defaultChallengeCount
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}
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if conf.Size <= 0 {
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conf.Size = defaultChallengeSize
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}
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if conf.Difficulty <= 0 {
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conf.Difficulty = defaultDifficulty
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}
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if conf.Expires <= 0 {
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conf.Expires = defaultExpires
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}
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now := time.Now().UnixNano() / int64(time.Millisecond)
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expires := now + int64(conf.Expires/time.Millisecond)
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payload := ChallengePayload{
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Nonce: RandomHex(defaultNonceLength),
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Count: conf.Count,
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Size: conf.Size,
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Difficulty: conf.Difficulty,
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Expires: expires,
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IssuedAt: now,
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Scope: scope,
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}
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payloadBytes, err := json.Marshal(payload)
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if err != nil {
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return nil, err
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}
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token := jwtSign(payloadBytes, secret)
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resp := &ChallengeResponse{
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Token: token,
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Expires: expires,
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}
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resp.Challenge.C = conf.Count
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resp.Challenge.S = conf.Size
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resp.Challenge.D = conf.Difficulty
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return resp, nil
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}
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// VerifyChallengeSolutions verifies client submitted solutions
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func VerifyChallengeSolutions(token string, solutions []int, secret []byte, expectedScope string) (*ChallengePayload, error) {
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payloadBytes, err := jwtVerify(token, secret)
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if err != nil {
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return nil, errors.New(errInvalidToken)
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}
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var payload ChallengePayload
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if err := json.Unmarshal(payloadBytes, &payload); err != nil {
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return nil, errors.New(errInvalidToken)
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}
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if expectedScope != "" && payload.Scope != expectedScope {
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return nil, errors.New(errScopeMismatch)
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}
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now := time.Now().UnixNano() / int64(time.Millisecond)
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if payload.Expires < now {
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return nil, errors.New(errExpired)
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}
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if len(solutions) != payload.Count {
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return nil, errors.New(errInvalidSolutions)
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}
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tokenFnv := fnv1a(token)
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for i := 0; i < payload.Count; i++ {
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idxStr := strconv.Itoa(i + 1)
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saltSeed := fnv1aResume(tokenFnv, idxStr)
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targetSeed := fnv1aResume(saltSeed, "d")
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salt := prngFromHash(saltSeed, payload.Size)
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target := prngFromHash(targetSeed, payload.Difficulty)
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hashInput := salt + strconv.Itoa(solutions[i])
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hashBytes := sha256.Sum256([]byte(hashInput))
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hashHex := hex.EncodeToString(hashBytes[:])
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if !strings.HasPrefix(hashHex, target) {
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return nil, errors.New(errInvalidSolution)
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}
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}
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return &payload, nil
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}
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// Solve is a utility function to solve a challenge (mainly used for tests and reference implementation)
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func Solve(token string, count, size, difficulty int) []int {
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solutions := make([]int, count)
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tokenFnv := fnv1a(token)
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for i := 0; i < count; i++ {
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idxStr := strconv.Itoa(i + 1)
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saltSeed := fnv1aResume(tokenFnv, idxStr)
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targetSeed := fnv1aResume(saltSeed, "d")
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salt := prngFromHash(saltSeed, size)
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target := prngFromHash(targetSeed, difficulty)
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for nonce := 0; nonce < 1000000; nonce++ {
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hashInput := salt + strconv.Itoa(nonce)
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hashBytes := sha256.Sum256([]byte(hashInput))
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hashHex := hex.EncodeToString(hashBytes[:])
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if strings.HasPrefix(hashHex, target) {
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solutions[i] = nonce
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break
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}
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}
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}
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return solutions
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}
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