[RFC-0002] Add auth specification for Helm OCI

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

rfcs/0002-helm-oci/README.md

@@ -4,7 +4,7 @@
 
 **Creation date:** 2022-03-30
 
-**Last update:** 2022-06-07
+**Last update:** 2022-08-24
 
 ## Summary
 
@@ -37,7 +37,43 @@ When not specified, the `spec.type` field defaults to `default` which preserve t
 
 When the `spec.type` field is set to `oci`, the `spec.url` field must be prefixed with `oci://` (to follow the Helm conventions).
 For `oci://` URLs, source-controller will use the Helm SDK and the `oras` library to connect to the OCI remote storage.
-For authentication, the controller will use Kubernetes secrets of `kubernetes.io/dockerconfigjson` type.
+
+### Pull charts from private repositories
+
+#### Basic auth
+
+For private repositories hosted on GitHub, Quay, self-hosted Docker Registry and others,
+the credentials can be supplied with:
+
+```yaml
+spec:
+  secretRef:
+    name: regcred
+```
+
+The `secretRef` points to a Kubernetes secret in the same namespace as the `HelmRepository`.
+The secret type must be `kubernetes.io/dockerconfigjson`:
+
+```shell
+kubectl create secret docker-registry regcred \
+  --docker-server=<your-registry-server> \
+  --docker-username=<your-name> \
+  --docker-password=<your-pword>
+```
+
+#### OIDC auth
+
+When Flux runs on AKS, EKS or GKE, an IAM role (that grants read-only access to ACR, ECR or GCR)
+can be used to bind the `source-controller` to the IAM role.
+
+```yaml
+spec:
+  provider: azure
+```
+
+The provider accepts the following values: `generic`, `aws`, `azure` and `gcp`. When the provider is
+not specified, it defaults to `generic`. When the provider is set to `aws`, `azure` or `gcp`, the
+controller will use a specific cloud SDK for authentication purposes.
 
 ### User Stories
 
@@ -181,3 +217,4 @@ The feature is enabled by default.
 ### TODOs
 
 * [Add support for container registries with self-signed TLS certs](https://github.com/fluxcd/source-controller/issues/723)
+* [Enable contextual login in OCI HelmRepository](https://github.com/fluxcd/source-controller/pull/873)