Add comprehensive security tests for OWASP A02, A05, A07, and A08 categories

- Implemented tests for Cryptographic Failures (A02) to ensure proper handling of sensitive data, secure algorithms, and key management.
- Added tests for Security Misconfiguration (A05) to validate production configurations, security headers, CORS settings, and feature management.
- Developed tests for Authentication Failures (A07) to enforce strong password policies, rate limiting, session management, and MFA support.
- Created tests for Software and Data Integrity Failures (A08) to verify artifact signatures, SBOM integrity, attestation chains, and feed updates.

docs/modules/attestor/proof-spine-algorithm.md

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+# Proof Spine Assembly Algorithm
+
+> **Sprint:** SPRINT_0501_0004_0001
+> **Module:** Attestor / ProofChain
+
+## Overview
+
+The Proof Spine is the cryptographic backbone of StellaOps' proof chain. It aggregates evidence, reasoning, and VEX statements into a single merkle-rooted bundle that can be verified independently.
+
+## Architecture
+
+```
+┌─────────────────────────────────────────────────────────────────────────────┐
+│                         PROOF SPINE STRUCTURE                               │
+├─────────────────────────────────────────────────────────────────────────────┤
+│                                                                             │
+│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐    │
+│  │ SBOMEntryID  │  │ EvidenceID[] │  │ ReasoningID  │  │ VEXVerdictID │    │
+│  │ (leaf 0)     │  │ (leaves 1-N) │  │ (leaf N+1)   │  │ (leaf N+2)   │    │
+│  └──────┬───────┘  └──────┬───────┘  └──────┬───────┘  └──────┬───────┘    │
+│         │                 │                 │                 │            │
+│         └─────────────────┴─────────────────┴─────────────────┘            │
+│                                    │                                        │
+│                                    ▼                                        │
+│                    ┌───────────────────────────────┐                        │
+│                    │     MERKLE TREE BUILDER       │                        │
+│                    │  - SHA-256 hash function      │                        │
+│                    │  - Lexicographic sorting      │                        │
+│                    │  - Power-of-2 padding         │                        │
+│                    └───────────────┬───────────────┘                        │
+│                                    │                                        │
+│                                    ▼                                        │
+│                    ┌───────────────────────────────┐                        │
+│                    │      ProofBundleID (Root)     │                        │
+│                    │  sha256:<64-hex-chars>        │                        │
+│                    └───────────────────────────────┘                        │
+│                                                                             │
+└─────────────────────────────────────────────────────────────────────────────┘
+```
+
+## Algorithm Specification
+
+### Input
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `sbomEntryId` | string | Content-addressed ID of the SBOM entry |
+| `evidenceIds` | string[] | Array of evidence statement IDs |
+| `reasoningId` | string | ID of the reasoning/policy match statement |
+| `vexVerdictId` | string | ID of the VEX verdict statement |
+
+### Output
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `proofBundleId` | string | Merkle root in format `sha256:<64-hex>` |
+
+### Pseudocode
+
+```
+FUNCTION BuildProofBundleMerkle(sbomEntryId, evidenceIds[], reasoningId, vexVerdictId):
+    
+    // Step 1: Prepare leaves in deterministic order
+    leaves = []
+    leaves.append(SHA256(UTF8.GetBytes(sbomEntryId)))
+    
+    // Step 2: Sort evidence IDs lexicographically
+    sortedEvidenceIds = evidenceIds.Sort(StringComparer.Ordinal)
+    FOR EACH evidenceId IN sortedEvidenceIds:
+        leaves.append(SHA256(UTF8.GetBytes(evidenceId)))
+    
+    leaves.append(SHA256(UTF8.GetBytes(reasoningId)))
+    leaves.append(SHA256(UTF8.GetBytes(vexVerdictId)))
+    
+    // Step 3: Pad to power of 2 (duplicate last leaf)
+    WHILE NOT IsPowerOfTwo(leaves.Length):
+        leaves.append(leaves[leaves.Length - 1])
+    
+    // Step 4: Build tree bottom-up
+    currentLevel = leaves
+    WHILE currentLevel.Length > 1:
+        nextLevel = []
+        FOR i = 0 TO currentLevel.Length STEP 2:
+            left = currentLevel[i]
+            right = currentLevel[i + 1]
+            parent = SHA256(left || right)  // Concatenate then hash
+            nextLevel.append(parent)
+        currentLevel = nextLevel
+    
+    // Step 5: Return root as formatted ID
+    RETURN "sha256:" + HexEncode(currentLevel[0])
+```
+
+## Determinism Invariants
+
+| Invariant | Rule | Rationale |
+|-----------|------|-----------|
+| Evidence Ordering | Lexicographic (byte comparison) | Reproducible across platforms |
+| Hash Function | SHA-256 only | No algorithm negotiation |
+| Padding | Duplicate last leaf | Not zeros, preserves tree structure |
+| Concatenation | Left `\|\|` Right | Consistent ordering |
+| String Encoding | UTF-8 | Cross-platform compatibility |
+| ID Format | `sha256:<lowercase-hex>` | Canonical representation |
+
+## Example
+
+### Input
+
+```json
+{
+  "sbomEntryId": "sha256:abc123...",
+  "evidenceIds": [
+    "sha256:evidence-cve-2024-0001...",
+    "sha256:evidence-reachability...",
+    "sha256:evidence-sbom-component..."
+  ],
+  "reasoningId": "sha256:reasoning-policy...",
+  "vexVerdictId": "sha256:vex-not-affected..."
+}
+```
+
+### Processing
+
+1. **Leaf 0**: `SHA256("sha256:abc123...")` → SBOM
+2. **Leaf 1**: `SHA256("sha256:evidence-cve-2024-0001...")` → Evidence (sorted first)
+3. **Leaf 2**: `SHA256("sha256:evidence-reachability...")` → Evidence
+4. **Leaf 3**: `SHA256("sha256:evidence-sbom-component...")` → Evidence
+5. **Leaf 4**: `SHA256("sha256:reasoning-policy...")` → Reasoning
+6. **Leaf 5**: `SHA256("sha256:vex-not-affected...")` → VEX
+7. **Padding**: Duplicate leaf 5 to get 8 leaves (power of 2)
+
+### Tree Structure
+
+```
+                    ROOT
+                   /    \
+                  H1     H2
+                 / \    / \
+               H3   H4  H5  H6
+              / \  / \ / \ / \
+             L0 L1 L2 L3 L4 L5 L5 L5  (padded)
+```
+
+### Output
+
+```
+sha256:7f83b1657ff1fc53b92dc18148a1d65dfc2d4b1fa3d677284addd200126d9069
+```
+
+## Cross-Platform Verification
+
+### Test Vector
+
+For cross-platform compatibility testing, use this known test vector:
+
+**Input:**
+```json
+{
+  "sbomEntryId": "sha256:0000000000000000000000000000000000000000000000000000000000000001",
+  "evidenceIds": [
+    "sha256:0000000000000000000000000000000000000000000000000000000000000002",
+    "sha256:0000000000000000000000000000000000000000000000000000000000000003"
+  ],
+  "reasoningId": "sha256:0000000000000000000000000000000000000000000000000000000000000004",
+  "vexVerdictId": "sha256:0000000000000000000000000000000000000000000000000000000000000005"
+}
+```
+
+All implementations (C#, Go, Rust, TypeScript) must produce the same root hash.
+
+## Verification
+
+To verify a proof bundle:
+
+1. Obtain all constituent statements (SBOM, Evidence, Reasoning, VEX)
+2. Extract their content-addressed IDs
+3. Re-compute the merkle root using the algorithm above
+4. Compare with the claimed `proofBundleId`
+
+If the roots match, the bundle is valid and all statements are bound to this proof.
+
+## API
+
+### C# Interface
+
+```csharp
+public interface IProofSpineAssembler
+{
+    /// <summary>
+    /// Assembles a proof spine from its constituent statements.
+    /// </summary>
+    ProofSpineResult Assemble(ProofSpineInput input);
+}
+
+public record ProofSpineInput
+{
+    public required string SbomEntryId { get; init; }
+    public required IReadOnlyList<string> EvidenceIds { get; init; }
+    public required string ReasoningId { get; init; }
+    public required string VexVerdictId { get; init; }
+}
+
+public record ProofSpineResult
+{
+    public required string ProofBundleId { get; init; }
+    public required byte[] MerkleRoot { get; init; }
+    public required IReadOnlyList<byte[]> LeafHashes { get; init; }
+}
+```
+
+## Related Documentation
+
+- [Proof and Evidence Chain Technical Reference](../product-advisories/14-Dec-2025%20-%20Proof%20and%20Evidence%20Chain%20Technical%20Reference.md) - §2.4, §4.2, §9
+- [Content-Addressed IDs](./content-addressed-ids.md)
+- [DSSE Predicates](./dsse-predicates.md)