📖 Document OLMv1 permission model (#1380)

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Author: rashmi43

docs/concepts/permission-model.md

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+#### OLMv1 Permission Model
+
+Here we aim to describe the OLMv1 permission model. OLMv1 itself does not have cluster-wide admin permissions. Therefore, each cluster extension must specify a service account with sufficient permissions to install and manage it. While this service account is distinct from any service account defined in the bundle, it will need sufficient privileges to create and assign the required RBAC. Therefore, the cluster extension service account's privileges would be a superset of the privileges required by the service account in the bundle.
+
+To understand the permission model, lets see the scope of the the service accounts associated with ClusterExtension deployment:
+
+#### Service Account associated with the ClusterExtension CR
+
+1) The ClusterExtension CR defines a service account to deploy and manage the ClusterExtension lifecycle and can be derived using the [document](../howto/derive-service-account.md). It is specified in the ClusterExtension [yaml](../tutorials/install-extension#L71) while deploying a ClusterExtension.
+2) The purpose of the service account specified in the ClusterExtension spec is to manage the cluster extension lifecycle. Its permissions are the cumulative of the permissions required for managing the cluster extension lifecycle and any RBAC that maybe included in the extension bundle.
+3) Since the extension bundle contains its own RBAC, it means the ClusterExtension service account requires either:
+- the same set of permissions that are defined in the RBAC that it is trying to create.
+- bind/escalate verbs for RBAC, see https://kubernetes.io/docs/reference/access-authn-authz/rbac/#privilege-escalation-prevention-and-bootstrapping
+
+#### Service Account/(s) part of the Extension Bundle
+1) The contents of the extension bundle may contain more service accounts and RBAC.
+2) The OLMv1 operator-controller creates the service account/(s) defined as part of the extension bundle with the required RBAC for the controller business logic.
+
+##### Example:
+
+Lets consider deployment of the ArgoCD operator. The ClusterExtension ClusterResource specifies a service account as part of its spec, usually denoted as the ClusterExtension installer service account. 
+The ArgoCD operator specifies the `argocd-operator-controller-manager` [service account](https://github.com/argoproj-labs/argocd-operator/blob/da6b8a7e68f71920de9545152714b9066990fc4b/deploy/olm-catalog/argocd-operator/0.6.0/argocd-operator.v0.6.0.clusterserviceversion.yaml#L1124) with necessary RBAC for the bundle resources and OLMv1 creates it as part of this extension bundle deployment.
+
+The extension bundle CSV contains the [permissions](https://github.com/argoproj-labs/argocd-operator/blob/da6b8a7e68f71920de9545152714b9066990fc4b/deploy/olm-catalog/argocd-operator/0.6.0/argocd-operator.v0.6.0.clusterserviceversion.yaml#L1091) and [cluster permissions](https://github.com/argoproj-labs/argocd-operator/blob/da6b8a7e68f71920de9545152714b9066990fc4b/deploy/olm-catalog/argocd-operator/0.6.0/argocd-operator.v0.6.0.clusterserviceversion.yaml#L872) allow the operator to manage and run the controller logic. These permissions are assigned to the `argocd-operator-controller-manager` service account when the operator bundle is deployed.
+
+OLM v1 will assign all the RBAC specified in the extension bundle to the above service account.
+The ClusterExtension installer service account will need all the RBAC specified for the `argocd-operator-controller-manager` and additional RBAC for deploying the ClusterExtension.
+
+**Note**: The ClusterExtension permissions are not propogated to the deployment. The ClusterExtension service account and the bundle's service accounts have different purposes and naming conflicts between the two service accounts can lead to failure of ClusterExtension deployment.