Attempt to support unconfigured kerberos and weird Mac cred cache

cmd_credential.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"syscall"
 	"time"
@@ -61,16 +62,31 @@ func credFetch(server, username string, noKerberos bool, logf func(string, ...an
 func credFetchKerberos(url string, logf func(string, ...any)) ([]byte, error) {
 	krb5cfgPath := krb5ConfigPath()
 	logf("Kerberos: loading config from %s", krb5cfgPath)
-	krb5cfg, err := config.Load(krb5cfgPath)
+	var krb5cfg *config.Config
+	if _, statErr := os.Stat(krb5cfgPath); os.IsNotExist(statErr) && os.Getenv("KRB5_CONFIG") == "" {
+		logf("Kerberos: %s not found, using default config (KDC discovery via DNS)", krb5cfgPath)
+		krb5cfg = config.New()
+		krb5cfg.LibDefaults.DNSLookupKDC = true
+	} else {
+		var err error
+		krb5cfg, err = config.Load(krb5cfgPath)
 		if err != nil {
 			return nil, fmt.Errorf("loading krb5 config: %w", err)
 		}
+	}
 
-	ccPath := ccachePath()
+	ccPath, err := ccachePath()
+	if err != nil {
+		return nil, err
+	}
 	logf("Kerberos: loading credential cache from %s", ccPath)
 	ccache, err := credentials.LoadCCache(ccPath)
 	if err != nil {
-		return nil, fmt.Errorf("no credential cache (%w) — run 'kinit'", err)
+		hint := "run 'kinit'"
+		if runtime.GOOS == "darwin" && os.Getenv("KRB5CCNAME") == "" {
+			hint = fmt.Sprintf("on macOS, run: kinit -c /tmp/krb5cc_%d", os.Getuid())
+		}
+		return nil, fmt.Errorf("no credential cache (%w) — %s", err, hint)
 	}
 
 	cl, err := krb5client.NewFromCCache(ccache, krb5cfg, krb5client.DisablePAFXFAST(true))
@@ -224,15 +240,25 @@ func krb5ConfigPath() string {
 	return cmp.Or(os.Getenv("KRB5_CONFIG"), "/etc/krb5.conf")
 }
 
-// ccachePath returns the path to the active Kerberos credential cache.
+// ccachePath returns the path to the active Kerberos credential cache, or an
-// Respects $KRB5CCNAME; strips the "FILE:" prefix if present.
+// error if $KRB5CCNAME names a non-file cache type that gokrb5 cannot read.
-// Non-file ccache types (API:, KEYRING:, DIR:) are not supported by gokrb5
+//
-// and will produce an error when LoadCCache is called.
+// On macOS, kinit defaults to API: caches. Work around it with:
-func ccachePath() string {
+//
+//	kinit -c /tmp/krb5cc_$(id -u)
+func ccachePath() (string, error) {
 	if v := os.Getenv("KRB5CCNAME"); v != "" {
-		return strings.TrimPrefix(v, "FILE:")
+		for _, prefix := range []string{"API:", "KEYRING:", "DIR:", "KCM:"} {
+			if strings.HasPrefix(v, prefix) {
+				return "", fmt.Errorf(
+					"credential cache type %s is not supported (gokrb5 requires a file-based cache)\n"+
+						"hint: re-run kinit with: kinit -c /tmp/krb5cc_%d",
+					prefix, os.Getuid())
 			}
-	return fmt.Sprintf("/tmp/krb5cc_%d", os.Getuid())
+		}
+		return strings.TrimPrefix(v, "FILE:"), nil
+	}
+	return fmt.Sprintf("/tmp/krb5cc_%d", os.Getuid()), nil
 }
 
 // ── Password prompt ────────────────────────────────────────────────────────────