backend: OIDC: Return error on state generation failure

backend/cmd/headlamp.go

@@ -914,14 +914,7 @@ func createHeadlampHandler(ctx context.Context, config *HeadlampConfig) http.Han
 		}
 
 		// state should be unique per request, cryptographically secure random, url safe
-		state, err := func() (string, error) {
-			b := make([]byte, 32)
-			if _, err := rand.Read(b); err != nil {
-				return "", fmt.Errorf("generating OIDC state: %w", err)
-			}
-
-			return base64.RawURLEncoding.EncodeToString(b), nil
-		}()
+		state, err := generateOidcState(rand.Reader)
 		if err != nil {
 			logger.Log(logger.LevelError, map[string]string{"cluster": cluster}, err, "failed to generate OIDC state")
 			http.Error(w, "failed to generate OIDC state", http.StatusInternalServerError)
@@ -1365,6 +1358,16 @@ func isLoopbackAddr(addr string) bool {
 	return ip != nil && ip.IsLoopback()
 }
 
+func generateOidcState(reader io.Reader) (string, error) {
+	b := make([]byte, 32)
+
+	if _, err := io.ReadFull(reader, b); err != nil {
+		return "", err
+	}
+
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}
+
 // allowedHosts returns the set of normalized host values that are considered
 // valid for the given listen address and port. All entries are lowercased and
 // host:port pairs are built with net.JoinHostPort so that IPv6 literals are

backend/cmd/headlamp_test.go

@@ -24,6 +24,7 @@ import (
 	"crypto/x509"
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -1830,6 +1831,41 @@ func TestOidcCallbackEmptyStateDoesNotLogStaleError(t *testing.T) {
 		"missing-state log must not carry a stale error from the outer createHeadlampHandler scope")
 }
 
+func TestGenerateOidcState(t *testing.T) {
+	t.Run("success", func(t *testing.T) {
+		stateBytes := make([]byte, 32)
+		for i := range stateBytes {
+			stateBytes[i] = byte(i)
+		}
+
+		state, err := generateOidcState(bytes.NewReader(stateBytes))
+		require.NoError(t, err)
+		assert.Equal(t, "AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8", state)
+	})
+
+	t.Run("failure", func(t *testing.T) {
+		state, err := generateOidcState(errReader{err: errors.New("rand failure")})
+
+		require.Error(t, err)
+		assert.Empty(t, state)
+	})
+
+	t.Run("short read", func(t *testing.T) {
+		state, err := generateOidcState(bytes.NewReader(make([]byte, 31)))
+
+		require.ErrorIs(t, err, io.ErrUnexpectedEOF)
+		assert.Empty(t, state)
+	})
+}
+
+type errReader struct {
+	err error
+}
+
+func (r errReader) Read([]byte) (int, error) {
+	return 0, r.err
+}
+
 func TestOIDCTokenRefreshMiddleware(t *testing.T) {
 	kubeConfigStore := kubeconfig.NewContextStore()
 	config := &HeadlampConfig{