Fix potential panic in audit during header formatting (#22694)

audit/options.go

@@ -5,6 +5,7 @@ package audit
 
 import (
 	"errors"
+	"reflect"
 	"strings"
 	"time"
 )
@@ -150,9 +151,13 @@ func WithHMACAccessor(h bool) Option {
 }
 
 // WithHeaderFormatter provides an Option to supply a HeaderFormatter.
+// If the HeaderFormatter interface supplied is nil (type or value), the option will not be applied.
 func WithHeaderFormatter(f HeaderFormatter) Option {
 	return func(o *options) error {
-		o.withHeaderFormatter = f
+		if f != nil && !reflect.ValueOf(f).IsNil() {
+			o.withHeaderFormatter = f
+		}
+
 		return nil
 	}
 }

audit/options_test.go

@@ -4,6 +4,7 @@
 package audit
 
 import (
+	"context"
 	"testing"
 	"time"
 
@@ -361,6 +362,45 @@ func TestOptions_WithOmitTime(t *testing.T) {
 	}
 }
 
+// TestOptions_WithHeaderFormatter exercises the WithHeaderFormatter Option to
+// ensure it applies the option as expected under various circumstances.
+func TestOptions_WithHeaderFormatter(t *testing.T) {
+	tests := map[string]struct {
+		Value                    HeaderFormatter
+		ExpectedValue            HeaderFormatter
+		ShouldLeaveUninitialized bool
+	}{
+		"nil": {
+			Value:         nil,
+			ExpectedValue: nil,
+		},
+		"unassigned-interface": {
+			ShouldLeaveUninitialized: true,
+		},
+		"happy-path": {
+			Value:         &testHeaderFormatter{},
+			ExpectedValue: &testHeaderFormatter{},
+		},
+	}
+
+	for name, tc := range tests {
+		name := name
+		tc := tc
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			opts := &options{}
+			var f HeaderFormatter
+			if !tc.ShouldLeaveUninitialized {
+				f = tc.Value
+			}
+			applyOption := WithHeaderFormatter(f)
+			err := applyOption(opts)
+			require.NoError(t, err)
+			require.Equal(t, tc.ExpectedValue, opts.withHeaderFormatter)
+		})
+	}
+}
+
 // TestOptions_Default exercises getDefaultOptions to assert the default values.
 func TestOptions_Default(t *testing.T) {
 	opts := getDefaultOptions()
@@ -485,3 +525,12 @@ func TestOptions_Opts(t *testing.T) {
 		})
 	}
 }
+
+// testHeaderFormatter is a stub to prevent the need to import the vault package
+// to bring in vault.AuditedHeadersConfig for testing.
+type testHeaderFormatter struct{}
+
+// ApplyConfig satisfied the HeaderFormatter interface for testing.
+func (f *testHeaderFormatter) ApplyConfig(ctx context.Context, headers map[string][]string, salter Salter) (result map[string][]string, retErr error) {
+	return nil, nil
+}

changelog/22694.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+audit: Prevent panic due to nil pointer receiver for audit header formatting.
+```