test: verify default TLS key exchanges across Go versions

README.md

@@ -31,6 +31,27 @@ require this path, and rewrite the imports.
 The repository was renamed from `pgsty/minio-pkg` on 2026-08-02. GitHub redirects
 the old path, but pin the new one.
 
+## Go and TLS compatibility
+
+The library retains its Go 1.26 floor and is also tested with Go 1.27. Runtime
+defaults depend on the consuming application's Go version and `GODEBUG`, not
+just this library's `go.mod`. The web-environment client leaves TLS key exchange
+at Go defaults; LDAP and OIDC helpers also preserve caller-supplied TLS settings.
+For default-configured TLS, `GODEBUG=tlsmlkem=0` disables hybrid key exchanges;
+`GODEBUG=tlssecpmlkem=0` disables only the SecP hybrids and retains X25519MLKEM768.
+These settings preserve certificate verification.
+
+On macOS, applications targeting Go 1.27 replace Keychain trust with on-disk
+roots and Go's verifier when either `SSL_CERT_FILE` or `SSL_CERT_DIR` is set.
+Stale or incomplete CA paths can break previously trusted connections; unset
+inherited values to restore Keychain trust. Explicit CAs supplied to
+`certs.GetRootCAs` remain additive to the selected root pool.
+An application still targeting Go 1.26 retains the
+old platform default unless it opts in with
+`GODEBUG=x509sslcertoverrideplatform=1`. The Windows loader in this package reads
+the Windows ROOT store directly and is unchanged. See the
+[Go release notes](https://go.dev/doc/go1.27).
+
 ## Versioning
 
 Tags follow upstream's numbering so it is obvious which release a version is

env/web_env_tls_test.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2026 Pigsty
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+package env
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"strings"
+	"testing"
+)
+
+func TestWebEnvTLSKeyExchangeDefaults(t *testing.T) {
+	for _, debug := range []string{"tlsmlkem=0", "tlsmlkem=1"} {
+		t.Run(debug, func(t *testing.T) {
+			t.Setenv("GODEBUG", debug)
+			hellos := make(chan []tls.CurveID, 1)
+			server := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+				_, _ = io.WriteString(w, "lab-value")
+			}))
+			server.TLS = &tls.Config{GetConfigForClient: func(hello *tls.ClientHelloInfo) (*tls.Config, error) {
+				select {
+				case hellos <- slices.Clone(hello.SupportedCurves):
+				default:
+				}
+				return nil, nil
+			}}
+			server.StartTLS()
+			defer server.Close()
+			roots := x509.NewCertPool()
+			roots.AddCert(server.Certificate())
+			previousRoots := globalRootCAs
+			RegisterGlobalCAs(roots)
+			t.Cleanup(func() { RegisterGlobalCAs(previousRoots) })
+			endpoint := "env+tls://local:" + strings.Repeat("x", 64) + "@" + server.Listener.Addr().String()
+			value, _, _, err := getEnvValueFromHTTP(endpoint, "lab-key")
+			if err != nil || value != "lab-value" {
+				t.Fatalf("value %q, error %v", value, err)
+			}
+			curves := <-hellos
+			if got, want := slices.Contains(curves, tls.X25519MLKEM768), debug == "tlsmlkem=1"; got != want {
+				t.Errorf("ML-KEM offered = %v, want %v; curves %v", got, want, curves)
+			}
+		})
+	}
+}