Add 5 new cybersecurity skills batch 2 - oauth token theft, binary exploitation, STIX2 sharing, linux audit logs, timestomping detection

skills/implementing-security-information-sharing-with-stix2/references/api-reference.md

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+# API Reference: Security Information Sharing with STIX 2.1
+
+## stix2 Python Library
+```bash
+pip install stix2 taxii2-client
+```
+
+### Create Objects
+```python
+from stix2 import Indicator, Malware, Relationship, Bundle, Identity
+
+identity = Identity(name="My SOC", identity_class="organization")
+
+indicator = Indicator(
+    name="Malicious IP",
+    pattern="[ipv4-addr:value = '198.51.100.42']",
+    pattern_type="stix",
+    valid_from="2025-01-01T00:00:00Z",
+    created_by_ref=identity.id,
+)
+
+malware = Malware(name="EvilRAT", malware_types=["trojan"], is_family=True)
+
+rel = Relationship(source_ref=indicator.id, target_ref=malware.id,
+                   relationship_type="indicates")
+
+bundle = Bundle(objects=[identity, indicator, malware, rel])
+print(bundle.serialize(pretty=True))
+```
+
+### Validate and Parse
+```python
+import stix2
+
+parsed = stix2.parse(json_string, allow_custom=True)
+print(parsed.type, len(parsed.objects))
+```
+
+## STIX 2.1 Object Types
+| Type | Description |
+|------|------------|
+| indicator | IOC with STIX pattern |
+| malware | Malware family/sample |
+| campaign | Named threat campaign |
+| threat-actor | Threat group |
+| attack-pattern | TTP (ATT&CK technique) |
+| relationship | Link between objects |
+| sighting | Observation of indicator |
+| identity | Organization/individual |
+
+## TAXII 2.1 Publishing
+```python
+from taxii2client.v21 import Collection
+
+collection = Collection(
+    "https://taxii.server.com/taxii2/collections/abc-123/",
+    user="api_user", password="api_pass"
+)
+collection.add_objects(bundle.serialize())
+```
+
+## TLP Marking Definitions
+| TLP | stix2 Constant |
+|-----|---------------|
+| TLP:CLEAR | stix2.TLP_WHITE |
+| TLP:GREEN | stix2.TLP_GREEN |
+| TLP:AMBER | stix2.TLP_AMBER |
+| TLP:RED | stix2.TLP_RED |
+
+## STIX Pattern Examples
+| Type | Pattern |
+|------|---------|
+| IPv4 | `[ipv4-addr:value = '1.2.3.4']` |
+| Domain | `[domain-name:value = 'evil.com']` |
+| SHA-256 | `[file:hashes.'SHA-256' = 'abc...']` |
+| URL | `[url:value = 'https://evil.com/mal']` |
+| Email | `[email-addr:value = 'bad@evil.com']` |