fix: return 401 for expired oauth2 tokens (#18)

This change updates the OAuth2 middleware to return a 401 Unauthorized
response when a token is expired. The previous behavior of returning 400
was non-compliant. We've also added endpoints to introspect access
tokens.

cmd/server/main.go

@@ -30,6 +30,7 @@ func main() {
 	flag.Parse()
 
 	r := mux.NewRouter()
+	r.HandleFunc("/oauth2/token", auth.HandleOAuth2InspectToken).Methods(http.MethodGet)
 	r.HandleFunc("/oauth2/token", auth.HandleOAuth2).Methods(http.MethodPost)
 	r.HandleFunc("/auth", auth.HandleAuth).Methods(http.MethodPost)
 	r.HandleFunc("/auth/customsecurity/{customSchemeType}", auth.HandleCustomAuth).Methods(http.MethodGet)

internal/auth/oauth2.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -75,6 +76,38 @@ type OAuth2TokenResponse struct {
 	ExpiresIn    int    `json:"expires_in"`
 }
 
+func HandleOAuth2InspectToken(w http.ResponseWriter, r *http.Request) {
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "  ")
+	w.Header().Set("Content-Type", "application/json")
+
+	authz := r.Header.Get("Authorization")
+	if authz == "" {
+		http.Error(w, `{"error": "unauthorized"}`, http.StatusUnauthorized)
+		return
+	}
+	if !strings.HasPrefix(authz, "Bearer ") {
+		http.Error(w, `{"error": "invalid authorization"}`, http.StatusBadRequest)
+		return
+	}
+
+	token := authz[len("Bearer "):]
+	claims, err := ParseToken(token)
+	if err != nil {
+		http.Error(w, `{"error": "invalid token"}`, http.StatusBadRequest)
+		return
+	}
+
+	updatedExpiry := GetTokenExpiry(claims)
+
+	claims["exp"] = float64(updatedExpiry.Unix())
+
+	if err := enc.Encode(claims); err != nil {
+		http.Error(w, `{"error": "failed to encode response"}`, http.StatusInternalServerError)
+		return
+	}
+}
+
 func HandleOAuth2(w http.ResponseWriter, r *http.Request) {
 	enc := json.NewEncoder(w)
 	enc.SetIndent("", "  ")
@@ -165,6 +198,10 @@ func HandleOAuth2(w http.ResponseWriter, r *http.Request) {
 
 	now := time.Now()
 	expires := now.Add(time.Hour)
+	forcedExpiry := r.Header.Get("x-oauth2-expire-at")
+	if exp, err := time.Parse(time.RFC3339, forcedExpiry); err == nil {
+		expires = exp
+	}
 
 	accessTokenID := gofakeit.UUID()
 	accessTokenClaims := jwt.MapClaims{
@@ -248,6 +285,24 @@ func RefreshToken(refreshClaims jwt.MapClaims) {
 	tokenDB.Store(tokenID, expiry)
 }
 
+func GetTokenExpiry(tokenClaims jwt.MapClaims) time.Time {
+	tokenDBLastAccess.Store(time.Now())
+
+	tokenID := tokenClaims["id"].(string)
+
+	exp, found := tokenDB.Load(tokenID)
+	if found {
+		return exp.(time.Time)
+	}
+
+	expiryClaim, err := tokenClaims.GetExpirationTime()
+	if err != nil {
+		panic(err)
+	}
+
+	return expiryClaim.Time
+}
+
 func IsTokenExpired(tokenClaims jwt.MapClaims) bool {
 	tokenDBLastAccess.Store(time.Now())
 

internal/middleware/oauth2.go

@@ -31,7 +31,8 @@ func OAuth2(h http.Handler) http.Handler {
 		}
 
 		if auth.IsTokenExpired(claims) {
-			auth.SendOAuth2Error(w, auth.ErrCodeInvalidRequest, "token has expired")
+			w.Header().Set("Content-Type", "application/json")
+			http.Error(w, `{"error": "token has expired"}`, http.StatusUnauthorized)
 			return
 		}