fix: add missing temporal-cloud-encryption doc

docs/temporal-cloud-encryption.md

@@ -0,0 +1,106 @@
+# Temporal Cloud Payload Encryption
+
+Datafold supports two approaches for encrypting Temporal workflow payloads when using Temporal Cloud:
+
+1. **Built-in AES-256-GCM codec** — provide one or more base64-encoded keys via `global.temporal.encryption.keys`. No additional setup needed.
+2. **Custom codec class** — supply a Python file that implements the `temporalio.converter.PayloadCodec` interface. Use this when you need external key management (e.g. AWS KMS).
+
+---
+
+## Built-In AES-256-GCM Codec
+
+No custom file needed. Set keys in your CR or values:
+
+```yaml
+global:
+  temporal:
+    encryption:
+      activeKeyId: KEY_1
+      keys:
+        - id: KEY_1
+          valueSecret:
+            secretName: datafold-operator-secrets
+            keyName: temporalEncryptionKeyV1
+        - id: KEY_0
+          valueSecret:
+            secretName: datafold-operator-secrets
+            keyName: temporalEncryptionKeyV0
+```
+
+Generate a key with:
+
+```bash
+openssl rand -base64 32
+```
+
+Store it in a Kubernetes Secret:
+
+```bash
+kubectl create secret generic datafold-operator-secrets \
+  --from-literal=temporalEncryptionKeyV1="$(openssl rand -base64 32)" \
+  -n <YOUR_NAMESPACE>
+```
+
+---
+
+## Custom Codec Class (e.g. AWS KMS)
+
+### 1. Write the codec
+
+Create a Python file (e.g. `temporal_codec.py`) that implements the `temporalio.converter.PayloadCodec` interface:
+
+```python
+from temporalio.converter import PayloadCodec
+from temporalio.api.common.v1 import Payload
+from typing import Iterable
+
+class KMSCodec(PayloadCodec):
+    async def encode(self, payloads: Iterable[Payload]) -> list[Payload]:
+        # Encrypt each payload using your key provider (e.g. AWS KMS)
+        ...
+
+    async def decode(self, payloads: Iterable[Payload]) -> list[Payload]:
+        # Decrypt each payload using your key provider
+        ...
+```
+
+The module stem (`temporal_codec`) and class name (`KMSCodec`) must match the `codecClass` value in your configuration: `"temporal_codec:KMSCodec"`.
+
+### 2. Create the ConfigMap
+
+```bash
+kubectl create configmap acme-temporal-codec \
+  --from-file=temporal_codec.py=./temporal_codec.py \
+  -n <YOUR_NAMESPACE>
+```
+
+### 3. Reference the ConfigMap in your CR or values
+
+**Operator (DatafoldApplication CR):**
+
+```yaml
+spec:
+  global:
+    temporal:
+      encryption:
+        codecClass: "temporal_codec:KMSCodec"
+        customCodec:
+          configMapName: acme-temporal-codec
+          fileName: temporal_codec.py
+```
+
+**Direct Helm values:**
+
+```yaml
+global:
+  temporal:
+    encryption:
+      codecClass: "temporal_codec:KMSCodec"
+      customCodec:
+        configMapName: acme-temporal-codec
+        fileName: temporal_codec.py
+```
+
+The operator mounts the file from the ConfigMap into all Temporal containers at `/datafold/plugins/<fileName>`. The `TEMPORAL_CODEC_CLASS` environment variable is set automatically from `codecClass`.
+
+See the [full example CR](../examples/operator/acme-temporal-cloud-custom-codec.yaml) for a complete working configuration.