Implement HMAC-SHA256 signature generation and verification
This commit is contained in:
139
internal/imgcache/signature.go
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139
internal/imgcache/signature.go
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@@ -0,0 +1,139 @@
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package imgcache
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import (
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"crypto/hmac"
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"crypto/sha256"
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"encoding/base64"
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"errors"
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"fmt"
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"strconv"
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"time"
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)
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// Signature errors.
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var (
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ErrSignatureRequired = errors.New("signature required for non-whitelisted host")
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ErrSignatureInvalid = errors.New("invalid signature")
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ErrSignatureExpired = errors.New("signature has expired")
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ErrMissingExpiration = errors.New("signature expiration is required")
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)
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// Signer handles HMAC-SHA256 signature generation and verification.
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type Signer struct {
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secretKey []byte
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}
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// NewSigner creates a new Signer with the given secret key.
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func NewSigner(secretKey string) *Signer {
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return &Signer{
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secretKey: []byte(secretKey),
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}
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}
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// Sign generates an HMAC-SHA256 signature for the given image request.
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// The signature covers: host + path + query + width + height + format + expiration.
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func (s *Signer) Sign(req *ImageRequest) string {
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data := s.buildSignatureData(req)
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mac := hmac.New(sha256.New, s.secretKey)
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mac.Write([]byte(data))
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sig := mac.Sum(nil)
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return base64.URLEncoding.EncodeToString(sig)
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}
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// Verify checks if the signature on the request is valid and not expired.
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func (s *Signer) Verify(req *ImageRequest) error {
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// Check expiration first
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if req.Expires.IsZero() {
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return ErrMissingExpiration
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}
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if time.Now().After(req.Expires) {
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return ErrSignatureExpired
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}
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// Compute expected signature
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expected := s.Sign(req)
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// Constant-time comparison to prevent timing attacks
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if !hmac.Equal([]byte(req.Signature), []byte(expected)) {
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return ErrSignatureInvalid
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}
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return nil
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}
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// buildSignatureData creates the string to be signed.
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// Format: "host:path:query:width:height:format:expiration"
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func (s *Signer) buildSignatureData(req *ImageRequest) string {
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return fmt.Sprintf("%s:%s:%s:%d:%d:%s:%d",
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req.SourceHost,
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req.SourcePath,
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req.SourceQuery,
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req.Size.Width,
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req.Size.Height,
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req.Format,
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req.Expires.Unix(),
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)
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}
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// GenerateSignedURL creates a complete URL with signature and expiration.
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// Returns the path portion that should be appended to the base URL.
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func (s *Signer) GenerateSignedURL(req *ImageRequest, ttl time.Duration) (path string, sig string, exp int64) {
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// Set expiration
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req.Expires = time.Now().Add(ttl)
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exp = req.Expires.Unix()
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// Generate signature
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sig = s.Sign(req)
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req.Signature = sig
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// Build the size component
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var sizeStr string
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if req.Size.OriginalSize() {
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sizeStr = "orig"
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} else {
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sizeStr = fmt.Sprintf("%dx%d", req.Size.Width, req.Size.Height)
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}
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// Build the path
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path = fmt.Sprintf("/v1/image/%s%s/%s.%s",
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req.SourceHost,
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req.SourcePath,
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sizeStr,
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req.Format,
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)
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// Append query if present
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if req.SourceQuery != "" {
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// The query goes before the size segment in our URL scheme
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// So we need to rebuild the path
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path = fmt.Sprintf("/v1/image/%s%s?%s/%s.%s",
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req.SourceHost,
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req.SourcePath,
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req.SourceQuery,
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sizeStr,
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req.Format,
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)
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}
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return path, sig, exp
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}
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// ParseSignatureParams extracts signature and expiration from query parameters.
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func ParseSignatureParams(sig, expStr string) (signature string, expires time.Time, err error) {
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signature = sig
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if expStr == "" {
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return signature, time.Time{}, nil
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}
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expUnix, err := strconv.ParseInt(expStr, 10, 64)
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if err != nil {
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return "", time.Time{}, fmt.Errorf("invalid expiration: %w", err)
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}
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expires = time.Unix(expUnix, 0)
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return signature, expires, nil
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}
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295
internal/imgcache/signature_test.go
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295
internal/imgcache/signature_test.go
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@@ -0,0 +1,295 @@
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package imgcache
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import (
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"testing"
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"time"
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)
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func TestSigner_Sign(t *testing.T) {
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signer := NewSigner("test-secret-key")
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req := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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SourceQuery: "",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Expires: time.Unix(1704067200, 0), // Fixed timestamp for reproducibility
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}
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sig1 := signer.Sign(req)
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sig2 := signer.Sign(req)
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// Same input should produce same signature
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if sig1 != sig2 {
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t.Errorf("Sign() produced different signatures for same input: %q vs %q", sig1, sig2)
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}
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// Signature should be non-empty
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if sig1 == "" {
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t.Error("Sign() produced empty signature")
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}
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// Different input should produce different signature
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req2 := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/dog.jpg", // Different path
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SourceQuery: "",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Expires: time.Unix(1704067200, 0),
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}
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sig3 := signer.Sign(req2)
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if sig1 == sig3 {
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t.Error("Sign() produced same signature for different input")
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}
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}
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func TestSigner_Verify(t *testing.T) {
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signer := NewSigner("test-secret-key")
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tests := []struct {
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name string
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setup func() *ImageRequest
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wantErr error
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}{
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{
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name: "valid signature",
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setup: func() *ImageRequest {
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req := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Expires: time.Now().Add(1 * time.Hour),
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}
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req.Signature = signer.Sign(req)
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return req
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},
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wantErr: nil,
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},
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{
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name: "expired signature",
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setup: func() *ImageRequest {
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req := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Expires: time.Now().Add(-1 * time.Hour), // Expired
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}
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req.Signature = signer.Sign(req)
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return req
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},
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wantErr: ErrSignatureExpired,
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},
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{
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name: "invalid signature",
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setup: func() *ImageRequest {
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return &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Expires: time.Now().Add(1 * time.Hour),
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Signature: "invalid-signature",
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}
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},
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wantErr: ErrSignatureInvalid,
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},
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{
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name: "missing expiration",
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setup: func() *ImageRequest {
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return &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Signature: "some-signature",
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// Expires is zero
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}
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},
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wantErr: ErrMissingExpiration,
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},
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{
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name: "tampered request",
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setup: func() *ImageRequest {
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req := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Expires: time.Now().Add(1 * time.Hour),
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}
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req.Signature = signer.Sign(req)
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// Tamper with the request
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req.SourcePath = "/photos/secret.jpg"
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return req
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},
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wantErr: ErrSignatureInvalid,
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},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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req := tt.setup()
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err := signer.Verify(req)
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if tt.wantErr == nil {
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if err != nil {
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t.Errorf("Verify() unexpected error = %v", err)
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}
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} else {
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if err != tt.wantErr {
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t.Errorf("Verify() error = %v, wantErr %v", err, tt.wantErr)
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}
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}
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})
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}
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}
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func TestSigner_DifferentKeys(t *testing.T) {
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signer1 := NewSigner("secret-key-1")
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signer2 := NewSigner("secret-key-2")
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req := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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Expires: time.Now().Add(1 * time.Hour),
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}
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// Sign with key 1
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req.Signature = signer1.Sign(req)
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// Verify with key 1 should succeed
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if err := signer1.Verify(req); err != nil {
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t.Errorf("Verify() with same key failed: %v", err)
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}
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// Verify with key 2 should fail
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if err := signer2.Verify(req); err != ErrSignatureInvalid {
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t.Errorf("Verify() with different key should fail, got: %v", err)
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}
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}
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func TestGenerateSignedURL(t *testing.T) {
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signer := NewSigner("test-secret-key")
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req := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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SourceQuery: "",
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Size: Size{Width: 800, Height: 600},
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Format: FormatWebP,
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}
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ttl := 1 * time.Hour
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path, sig, exp := signer.GenerateSignedURL(req, ttl)
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// Path should be correct format
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expectedPath := "/v1/image/cdn.example.com/photos/cat.jpg/800x600.webp"
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if path != expectedPath {
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t.Errorf("GenerateSignedURL() path = %q, want %q", path, expectedPath)
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}
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// Signature should be non-empty
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if sig == "" {
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t.Error("GenerateSignedURL() produced empty signature")
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}
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// Expiration should be approximately now + TTL
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expTime := time.Unix(exp, 0)
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expectedExp := time.Now().Add(ttl)
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if expTime.Sub(expectedExp) > time.Second {
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t.Errorf("GenerateSignedURL() exp time off by too much")
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}
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// Request should have been updated with signature and expiration
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if req.Signature != sig {
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t.Errorf("GenerateSignedURL() didn't update request signature")
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}
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}
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func TestGenerateSignedURL_OrigSize(t *testing.T) {
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signer := NewSigner("test-secret-key")
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req := &ImageRequest{
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SourceHost: "cdn.example.com",
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SourcePath: "/photos/cat.jpg",
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Size: Size{Width: 0, Height: 0}, // Original size
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Format: FormatPNG,
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}
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path, _, _ := signer.GenerateSignedURL(req, time.Hour)
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expectedPath := "/v1/image/cdn.example.com/photos/cat.jpg/orig.png"
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if path != expectedPath {
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t.Errorf("GenerateSignedURL() path = %q, want %q", path, expectedPath)
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}
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}
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func TestParseSignatureParams(t *testing.T) {
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tests := []struct {
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name string
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sig string
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expStr string
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wantSig string
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wantErr bool
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checkTime bool
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}{
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{
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name: "valid params",
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sig: "abc123",
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expStr: "1704067200",
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wantSig: "abc123",
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wantErr: false,
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},
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{
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name: "empty expiration",
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sig: "abc123",
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expStr: "",
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wantSig: "abc123",
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wantErr: false,
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},
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{
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name: "invalid expiration",
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sig: "abc123",
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expStr: "not-a-number",
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wantErr: true,
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},
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}
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for _, tt := range tests {
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t.Run(tt.name, func(t *testing.T) {
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sig, exp, err := ParseSignatureParams(tt.sig, tt.expStr)
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if tt.wantErr {
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if err == nil {
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t.Error("ParseSignatureParams() expected error, got nil")
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}
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return
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}
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if err != nil {
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t.Errorf("ParseSignatureParams() unexpected error = %v", err)
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return
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}
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if sig != tt.wantSig {
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t.Errorf("sig = %q, want %q", sig, tt.wantSig)
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}
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if tt.expStr != "" && exp.IsZero() {
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t.Error("exp should not be zero when expStr is provided")
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}
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})
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}
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}
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Block a user