test: add R-round regression and security suite

- fail-on-old regression tests for every shipped fix (R-rounds)
- fuzz targets (parseJWT, bearer), concurrency-stress, shuffle-flake guards
- coverage-closing contract tests (health-check backend, TLS-posture reuse)
- r154 ID-token fixture built from parts to avoid false-positive secret scan

review_r188_regression_test.go

@@ -0,0 +1,85 @@
+package traefikoidc
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"testing"
+
+	"github.com/gorilla/sessions"
+)
+
+// ============================================================================
+// R188: cross-chunk integrity binds chunked-token chunks to one another
+// ---------------------------------------------------------------------------
+// Each chunk is individually authenticated by its own securecookie MAC, so a
+// forged chunk is impossible; but an authentic-but-mixed set (a stale chunk
+// from an earlier session combined with the current session's chunks, where
+// counts still match) previously assembled silently into a wrong token that
+// only surfaced as a downstream JWT validation failure (→ forced re-auth).
+// New writes now store a SHA-256 of the assembled chunk string on every
+// chunk; processChunkedToken verifies it on read. Absent (old sessions) →
+// skipped, preserving backward compatibility.
+// Fail-on-old: a mixed set with matching count returns the reassembled
+// token; the integrity check now rejects it with an error.
+func TestR188_ChunkIntegrityDetectsMixedChunks(t *testing.T) {
+	cm := NewChunkManager(NewLogger(DefaultLogLevel))
+	config := TokenConfig{
+		Type:         "access",
+		MinLength:    5,
+		MaxLength:    100 * 1024,
+		MaxChunks:    25,
+		MaxChunkSize: maxCookieSize,
+	}
+
+	// Reassembled chunks form the opaque token "aaabbb"; but chunk 0's
+	// stored integrity was computed over a DIFFERENT string (a stale chunk
+	// from another session), so the set is mixed despite counts matching.
+	chunks := map[int]*sessions.Session{
+		0: {Values: map[interface{}]interface{}{
+			"token_chunk":     "aaa",
+			"token_total":     2,
+			"chunk_integrity": fmt.Sprintf("%x", sha256.Sum256([]byte("different-set"))),
+		}},
+		1: {Values: map[interface{}]interface{}{
+			"token_chunk": "bbb",
+			"token_total": 2,
+		}},
+	}
+
+	res := cm.GetToken("", false, chunks, config)
+	if res.Error == nil {
+		t.Fatalf("mixed chunk set must be rejected by chunk-integrity check; got token %q (old code returned it)", res.Token)
+	}
+}
+
+// A consistent set with a matching integrity value must still assemble.
+func TestR188_ChunkIntegrityValidSetStillSucceeds(t *testing.T) {
+	cm := NewChunkManager(NewLogger(DefaultLogLevel))
+	config := TokenConfig{
+		Type:         "access",
+		MinLength:    5,
+		MaxLength:    100 * 1024,
+		MaxChunks:    25,
+		MaxChunkSize: maxCookieSize,
+	}
+
+	chunks := map[int]*sessions.Session{
+		0: {Values: map[interface{}]interface{}{
+			"token_chunk":     "aaa",
+			"token_total":     2,
+			"chunk_integrity": fmt.Sprintf("%x", sha256.Sum256([]byte("aaabbb"))),
+		}},
+		1: {Values: map[interface{}]interface{}{
+			"token_chunk": "bbb",
+			"token_total": 2,
+		}},
+	}
+
+	res := cm.GetToken("", false, chunks, config)
+	if res.Error != nil {
+		t.Fatalf("valid coherent chunk set must assemble; got error: %v", res.Error)
+	}
+	if res.Token != "aaabbb" {
+		t.Fatalf("expected reassembled token %q, got %q", "aaabbb", res.Token)
+	}
+}