Change multi JWK Set min from 2 to 1

multiple.go

@@ -22,8 +22,8 @@ type MultipleJWKS struct {
 // map then many refresh requests would take place each time a JWT is processed, this should be rate limited by
 // RefreshRateLimit.
 func GetMultiple(multiple map[string]Options, options MultipleOptions) (multiJWKS *MultipleJWKS, err error) {
-	if multiple == nil || len(multiple) < 2 {
-		return nil, fmt.Errorf("multiple JWKS must have two or more remote JWK Set resources: %w", ErrMultipleJWKSSize)
+	if len(multiple) < 1 {
+		return nil, fmt.Errorf("multiple JWKS must have one or more remote JWK Set resources: %w", ErrMultipleJWKSSize)
 	}
 
 	if options.KeySelector == nil {

multiple_test.go

@@ -59,6 +59,46 @@ func TestMultipleJWKS(t *testing.T) {
 	}
 }
 
+func TestMultipleJWKSSingle(t *testing.T) {
+	server1 := createTestServer([]byte(jwks1))
+	defer server1.Close()
+
+	const (
+		collisionJWT = "eyJhbGciOiJFZERTQSIsImtpZCI6ImNvbGxpc2lvbktJRCIsInR5cCI6IkpXVCJ9.e30.WXKmhyHjHQFXZ8dXfj07RvwKAgHB3EdGU1jeKUEY-wajgsRsHuhnotX1WqDSlngwGerEitnIcdMGViW_HNUCAA"
+		uniqueJWT    = "eyJhbGciOiJFZERTQSIsImtpZCI6InVuaXF1ZUtJRCIsInR5cCI6IkpXVCJ9.e30.egdT5_vXYKIM7UfsyewYaR63tS9T9JvKwUJs7Srj6wG9JHXMvN9Ftq0rJGem07ESVtN5OtlcJOaMgSbtxnc6Bg"
+	)
+
+	m := map[string]keyfunc.Options{
+		server1.URL: {},
+	}
+
+	multiJWKS, err := keyfunc.GetMultiple(m, keyfunc.MultipleOptions{})
+	if err != nil {
+		t.Fatalf("failed to get multiple JWKS: %v", err)
+	}
+
+	token, err := jwt.Parse(collisionJWT, multiJWKS.Keyfunc)
+	if err != nil {
+		t.Fatalf("failed to parse collision JWT: %v", err)
+	}
+	if !token.Valid {
+		t.Fatalf("collision JWT is invalid")
+	}
+
+	token, err = jwt.Parse(uniqueJWT, multiJWKS.Keyfunc)
+	if err != nil {
+		t.Fatalf("failed to parse unique JWT: %v", err)
+	}
+	if !token.Valid {
+		t.Fatalf("unique JWT is invalid")
+	}
+
+	sets := multiJWKS.JWKSets()
+	if len(sets) != 1 {
+		t.Fatalf("expected 2 JWKS, got %d", len(sets))
+	}
+}
+
 func createTestServer(body []byte) *httptest.Server {
 	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")