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_r135_test.go

@@ -0,0 +1,68 @@
+package traefikoidc
+
+// R135 review-fix round regressions.
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"testing"
+)
+
+// TestValidate_IntrospectionOrOpaqueWithDCR_RequiresNoStaticSecret guards the
+// R135 fix: with Dynamic Client Registration enabled (and no static clientID),
+// the client secret is provisioned at runtime by the registrar, so the
+// Config.Validate() secret gate for requireTokenIntrospection /
+// allowOpaqueTokens must be skipped the same way the clientID gate is.
+// Fail-on-old: before the fix Validate() returned the introspect-secret error
+// for an otherwise-valid DCR + opaque-token config.
+func TestValidate_IntrospectionOrOpaqueWithDCR_RequiresNoStaticSecret(t *testing.T) {
+	c := r134ValidConfig()
+	c.ClientID = ""
+	c.ClientSecret = ""
+	c.RateLimit = CreateConfig().RateLimit
+	c.DynamicClientRegistration = &DynamicClientRegistrationConfig{Enabled: true}
+	c.AllowOpaqueTokens = true
+
+	if err := c.Validate(); err != nil {
+		t.Fatalf("expected valid DCR + opaque-token config, got %v", err)
+	}
+
+	// Sanity: without DCR the secret is still required.
+	c2 := r134ValidConfig()
+	c2.ClientSecret = ""
+	c2.AllowOpaqueTokens = true
+	if err := c2.Validate(); err == nil {
+		t.Fatal("expected clientSecret to be required for opaque-token introspection without DCR")
+	}
+}
+
+// TestNewClientAssertionSigner_RejectsWeakRSAKey guards the R135 fix: RFC
+// 7518 §3.3 requires RS*/PS* client-assertion keys of at least 2048 bits.
+// A smaller key signs locally but conformant IdPs reject it, so every
+// exchange/refresh/revocation fails at runtime — reject at construction.
+// Fail-on-old: a 1024-bit key was accepted by NewClientAssertionSigner.
+func TestNewClientAssertionSigner_RejectsWeakRSAKey(t *testing.T) {
+	for _, bits := range []int{1024, 1536} {
+		k, err := rsa.GenerateKey(rand.Reader, bits)
+		if err != nil {
+			t.Fatalf("keygen(%d): %v", bits, err)
+		}
+		der := x509.MarshalPKCS1PrivateKey(k)
+		pemBytes := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: der})
+		if _, err := NewClientAssertionSigner(pemBytes, "RS256", "kid-1"); err == nil {
+			t.Fatalf("expected %d-bit RSA key to be rejected, but it was accepted", bits)
+		}
+	}
+
+	strong, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("keygen(2048): %v", err)
+	}
+	der := x509.MarshalPKCS1PrivateKey(strong)
+	pemBytes := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: der})
+	if _, err := NewClientAssertionSigner(pemBytes, "RS256", "kid-1"); err != nil {
+		t.Fatalf("expected 2048-bit RSA key to be accepted, got %v", err)
+	}
+}