core/zero: use exit code 0 for bad requests

cmd/pomerium/main.go

@@ -6,6 +6,8 @@ import (
 	"errors"
 	"flag"
 	"fmt"
+	"os"
+	"strings"
 
 	"github.com/rs/zerolog"
 
@@ -40,6 +42,12 @@ func main() {
 	}
 
 	if err := runFn(ctx); err != nil && !errors.Is(err, context.Canceled) {
+		// if the error was due to a bad request, return 0 as the exit code
+		if strings.Contains(err.Error(), "bad request") {
+			log.Logger().WithLevel(zerolog.FatalLevel).Err(err).Msg("cmd/pomerium")
+			log.Writer.Close()
+			os.Exit(0)
+		}
 		log.Fatal().Err(err).Msg("cmd/pomerium")
 	}
 	log.Info(ctx).Msg("cmd/pomerium: exiting")

internal/log/multiwriter.go

@@ -1,6 +1,7 @@
 package log
 
 import (
+	"errors"
 	"io"
 	"slices"
 	"sync"
@@ -24,6 +25,19 @@ func (m *MultiWriter) Add(w io.Writer) {
 	m.mu.Unlock()
 }
 
+// Close closes the multi writer.
+func (m *MultiWriter) Close() error {
+	var err error
+	m.mu.Lock()
+	for _, w := range m.ws {
+		if c, ok := w.(io.Closer); ok {
+			err = errors.Join(err, c.Close())
+		}
+	}
+	m.mu.Unlock()
+	return err
+}
+
 // Remove removes a writer from the multi writer.
 func (m *MultiWriter) Remove(w io.Writer) {
 	m.mu.Lock()