fix: use standard JWT expiry claims for image proxy

src/routes/image.go

@@ -4,7 +4,6 @@ import (
 	"anonymousoverflow/src/types"
 	"fmt"
 	"os"
-	"time"
 
 	"github.com/gin-gonic/gin"
 	"github.com/go-resty/resty/v2"
@@ -45,11 +44,6 @@ func GetImage(c *gin.Context) {
 		return
 	}
 
-	if claims.Exp < time.Now().Unix() {
-		c.String(400, "Token expired")
-		return
-	}
-
 	// download the image
 	client := resty.New()
 	resp, err := client.R().Get(claims.ImageURL)

src/types/imageProxy.go

@@ -7,8 +7,5 @@ type ImageProxyClaims struct {
 
 	ImageURL string `json:"image_url"`
 
-	Iss int64 `json:"iss"`
-	Exp int64 `json:"exp"`
-
 	jwt.RegisteredClaims
 }

src/utils/images.go

@@ -42,11 +42,14 @@ func ReplaceImgTags(inHtml string) string {
 
 func generateImageProxyAuth(url string) (string, error) {
 	// generate a jwt with types.ImageProxyClaims
+	now := time.Now()
 	claims := types.ImageProxyClaims{
 		Action:   "imageProxy",
 		ImageURL: url,
-		Iss:      time.Now().Unix(),
-		Exp:      time.Now().Add(time.Minute).Unix(),
+		RegisteredClaims: jwt.RegisteredClaims{
+			IssuedAt:  jwt.NewNumericDate(now),
+			ExpiresAt: jwt.NewNumericDate(now.Add(time.Minute)),
+		},
 	}
 
 	token := jwt.NewWithClaims(jwt.SigningMethodHS512, claims)

src/utils/images_test.go

@@ -0,0 +1,51 @@
+package utils
+
+import (
+	"anonymousoverflow/src/types"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/golang-jwt/jwt/v4"
+)
+
+func TestImageProxyAuth(t *testing.T) {
+	const secret = "image-proxy-test-secret"
+	const imageURL = "https://example.com/image.png"
+	t.Setenv("JWT_SIGNING_SECRET", secret)
+
+	authorization, err := generateImageProxyAuth(imageURL)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	keyFunc := func(token *jwt.Token) (interface{}, error) {
+		return []byte(secret), nil
+	}
+	claims := &types.ImageProxyClaims{}
+	token, err := jwt.ParseWithClaims(authorization, claims, keyFunc)
+	if err != nil || !token.Valid {
+		t.Fatalf("fresh token rejected: %v", err)
+	}
+	if claims.Action != "imageProxy" || claims.ImageURL != imageURL {
+		t.Fatalf("unexpected claims: %+v", claims)
+	}
+	if claims.IssuedAt == nil || claims.ExpiresAt == nil {
+		t.Fatal("missing issue time or expiry")
+	}
+	if claims.ExpiresAt.Sub(claims.IssuedAt.Time) != time.Minute {
+		t.Fatal("token lifetime is not one minute")
+	}
+
+	originalTimeFunc := jwt.TimeFunc
+	t.Cleanup(func() { jwt.TimeFunc = originalTimeFunc })
+	jwt.TimeFunc = func() time.Time { return claims.ExpiresAt.Add(time.Second) }
+
+	token, err = jwt.ParseWithClaims(authorization, &types.ImageProxyClaims{}, keyFunc)
+	if !errors.Is(err, jwt.ErrTokenExpired) {
+		t.Fatalf("expected expiry error from ParseWithClaims, got %v", err)
+	}
+	if token != nil && token.Valid {
+		t.Fatal("expired token is valid")
+	}
+}