Add authentication and authorization

2026-07-28 01:01:12 +00:00 · 2018-09-01 09:40:30 -05:00
parent c05bcd23d9
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--- a/slides/k8s/authn-authz.md
+++ b/slides/k8s/authn-authz.md
@@ -0,0 +1,508 @@
+# Authentication and authorization
+
+*And first, a little refresher!*
+
+- Authentication = verifying the identity of a person
+
+  On a UNIX system, we can authenticate with login+password, SSH keys ...
+
+- Authorization = listing what they are allowed to do
+
+  On a UNIX system, this can include file permissions, sudoer entries ...
+
+- Sometimes abbreviated as "authn" and "authz"
+
+- In good modular systems, these things are decoupled
+
+   (so we can e.g. change a password or SSH key without having to reset access rights)
+
+---
+
+## Authentication in Kubernetes
+
+- When the API server receives a request, it tries to authenticate it
+
+  (it examines headers, certificates ... anything available)
+
+- Many authentication methods can be used simultaneously:
+
+  - TLS client certificates (that's what we've been doing with `kubectl` so far)
+
+  - bearer tokens (a secret token in the HTTP headers of the request)
+
+  - [HTTP basic auth](https://en.wikipedia.org/wiki/Basic_access_authentication) (carrying user and password in a HTTP header)
+
+  - authentication proxy (sitting in front of the API and setting trusted headers)
+
+- It's the job of the authentication method to produce:
+
+  - the user name
+  - the user ID
+  - a list of groups
+
+- The API server doesn't interpret these; it'll be the job of *authorizers*
+
+---
+
+## Anonymous requests
+
+- If any authentication method *rejects* a request, it's denied
+
+  (`401 Unauthorized` HTTP code)
+
+- If a request is neither accepted nor accepted by anyone, it's anonymous
+
+  - the user name is `system:anonymous`
+
+  - the list of groups is `[system:unauthenticated]`
+
+- By default, the anonymous user can't do anything
+
+  (that's what you get if you just `curl` the Kubernetes API)
+
+---
+
+## Authentication with TLS certificates
+
+- This is enabled in most Kubernetes deployments
+
+- The user name is derived from the `CN` in the client certificates
+
+- The groups are derived from the `O` fields in the client certificate
+
+- From the point of view of the Kubernetes API, users do not exist
+
+  (i.e. they are not stored in etcd or anywhere else)
+
+- Users can be created (and given membership to groups) independently of the API
+
+- The Kubernetes API can be set up to use your custom CA to validate client certs
+
+---
+
+class: extra-details
+
+## Viewing our admin certificate
+
+- Let's inspect the certificate we've been using all this time!
+
+.exercise[
+
+- This command will show the `CN` and `O` fields for our certificate:
+  ```bash
+  kubectl config view \
+          --raw \
+          -o json \
+          | jq -r .users[0].user[\"client-certificate-data\"] \
+          | base64 -d \
+          | openssl x509 -text \
+          | grep Subject:
+  ```
+
+]
+
+Let's break down that command together! 😅
+
+---
+
+class: extra-details
+
+## Breaking down the command
+
+- `kubectl config view` shows the Kubernetes user configuration
+- `--raw` includes certificate information (which shows as REDACTED otherwise)
+- `-o json` outputs the information in JSON format
+- `| jq ...` extracts the field with the user certificate (in base64)
+- `| base64 -d` decodes the base64 format (now we have a PEM file)
+- `| openssl x509 -text` parses the certificate and outputs it as plain text
+- `| grep Subject:` shows us the line that interests us
+
+→ We are user `kubernetes-admin`, in group `system:masters`.
+
+---
+
+## Authentication with tokens
+
+- Tokens are passed as HTTP headers:
+
+  `Authorization: Bearer and-then-here-comes-the-token`
+
+- Tokens can be validated through a number of different methods:
+
+  - static tokens hard-coded in a file on the API server
+
+  - [bootstrap tokens](https://kubernetes.io/docs/reference/access-authn-authz/bootstrap-tokens/) (special case to create a cluster or join nodes)
+
+  - [OpenID Connect tokens](https://kubernetes.io/docs/reference/access-authn-authz/authentication/#openid-connect-tokens) (to delegate authentication to compatible OAuth2 providers)
+
+  - service accounts (these deserve more details, coming right up!)
+
+---
+
+## Service accounts
+
+- A service account is a user that exists in the Kubernetes API
+
+  (it is visible with e.g. `kubectl get serviceaccounts`)
+
+- Service accounts can therefore be created / updated dynamically
+
+  (they don't require hand-editing a file and restarting the API server)
+
+- A service account is associated with a set of secrets
+
+  (the kind that you can view with `kubectl get secrets`)
+
+- Service accounts are generally used to grant permissions to applications, services ...
+
+  (as opposed to humans)
+
+---
+
+class: extra-details
+
+## Token authentication in practice
+
+- We are going to list existing service accounts
+
+- Then we will extract the token for a given service account
+
+- And we will use that token to authenticate with the API
+
+---
+
+class: extra-details
+
+## Listing service accounts
+
+.exercise[
+
+- The resource name is `serviceaccount` or `sa` in short:
+  ```bash
+  kubectl get sa
+  ```
+
+ ]
+
+ There should be just one service account in the default namespace: `default`.
+
+ ---
+
+ class: extra-details
+
+ ## Finding the secret
+
+ .exercise[
+
+ - List the secrets for the `default` service account:
+   ```bash
+   kubectl get sa default -o yaml
+   SECRET=$(kubectl get sa default -o json | jq -r .secrets[0].name)
+   ```
+
+]
+
+It should be named `default-token-XXXXX`.
+
+---
+
+class: extra-details
+
+## Extracting the token
+
+- The token is stored in the secret, wrapped with base64 encoding
+
+.exercise[
+
+- View the secret:
+  ```bash
+  kubectl get $SECRET -o yaml
+  ```
+
+- Extract the token and decode it:
+  ```bash
+  TOKEN=$(kubectl get secret $SECRET -o json \
+          | jq -r .data.token | base64 -d)
+  ```
+
+]
+
+---
+
+class: extra-details
+
+## Using the token
+
+- Let's send a request to the API, without and with the token
+
+.exercise[
+
+- Find the ClusterIP for the `kubernetes` service:
+  ```bash
+  kubectl get svc kubernetes
+  API=$(kubectl get svc kubernetes -o json | jq -r .spec.clusterIP)
+  ```
+
+- Connect without the token:
+  ```bash
+  curl -k https://$API
+  ```
+
+- Connect with the token:
+  ```bash
+  curl -k -H "Authorization: Bearer $TOKEN" https://$API
+  ```
+
+]
+
+---
+
+class: extra-details
+
+## Results
+
+- In both cases, we will get a "Forbidden" error
+
+- Without authentication, the user is `system:anonymous`
+
+- With authentication, it is shown as `system:serviceaccount:default:default`
+
+- The API "sees" us as a different user
+
+- But neither user has any right, so we can't do nothin'
+
+- Let's change that!
+
+---
+
+## Authorization in Kubernetes
+
+- There are multiple ways to grant permissions in Kubernetes, called [authorizers](https://kubernetes.io/docs/reference/access-authn-authz/authorization/#authorization-modules):
+
+  - [Node Authorization](https://kubernetes.io/docs/reference/access-authn-authz/node/) (used internally by kubelet; we can ignore it)
+
+  - [Attribute-based access control](https://kubernetes.io/docs/reference/access-authn-authz/abac/) (powerful but complex and static; ignore it too)
+
+  - [Webhook](https://kubernetes.io/docs/reference/access-authn-authz/webhook/) (each API request is submitted to an external service for approval)
+
+  - [Role-based access control](https://kubernetes.io/docs/reference/access-authn-authz/rbac/) (associates permissions to users dynamically)
+
+- The one we want is the last one, generally abbreviated as RBAC
+
+---
+
+## Role-based access control
+
+- RBAC allows to specify fine-grained permissions
+
+- Permissions are expressed as *rules*
+
+- A rule is a combination of:
+
+  - [verbs](https://kubernetes.io/docs/reference/access-authn-authz/authorization/#determine-the-request-verb) like create, get, list, update, delete ...
+
+  - resources (as in "API resource", like pods, nodes, services ...)
+
+  - resource names (to specify e.g. one specific pod instead of all pods)
+
+  - in some case, [subresources](https://kubernetes.io/docs/reference/access-authn-authz/rbac/#referring-to-resources) (e.g. logs are subresources of pods)
+
+---
+
+## From rules to roles to rolebindings
+
+- A *role* is an API object containing a list of *rules*
+
+  Example: role "external-load-balancer-configurator" can:
+  - [list, get] resources [endpoints, services, pods]
+  - [update] resources [services]
+
+- A *rolebinding* associates a role with a user
+
+  Example: rolebinding "external-load-balancer-configurator":
+  - associates user "external-load-balancer-configurator"
+  - with role "external-load-balancer-configurator"
+
+- Yes, there can be users, roles, and rolebindings with the same name
+
+- It's a good idea for 1-1-1 bindings; not so much for 1-N ones
+
+---
+
+## Cluster-scope permissions
+
+- API resources Role and RoleBinding are for objects within a namespace
+
+- We can also define API resources ClusterRole and ClusterRoleBinding
+
+- These are a superset, allowing to:
+
+  - specify actions on cluster-wide objects (like nodes)
+
+  - operate across all namespaces
+
+- We can create Role and RoleBinding resources within a namespaces
+
+- ClusterRole and ClusterRoleBinding resources are global
+
+---
+
+## Pods and service accounts
+
+- A pod can be associated to a service account
+
+  - by default, it is associated to the `default` service account
+
+  - as we've seen earlier, this service account has no permission anyway
+
+- The associated token is exposed into the pod's filesystem
+
+  (in `/var/run/secrets/kubernetes.io/serviceaccount/token`)
+
+- Standard Kubernetes tooling (like `kubectl`) will look for it there
+
+- So Kubernetes tools running in a pod will automatically use the service account
+
+---
+
+## In practice
+
+- We are going to create a service account
+
+- We will use an existing cluster role (`view`)
+
+- We will bind together this role and this service account
+
+- Then we will run a pod using that service account
+
+- In this pod, we will install `kubectl` and check our permissions
+
+---
+
+## Creating a service account
+
+- We will call the new service account `viewer`
+
+  (note that nothing prevents us from calling it `view`, like the role)
+
+.exercise[
+
+- Create the new service account:
+  ```bash
+  kubectl create serviceaccount viewer
+  ```
+
+- List service accounts now:
+  ```bash
+  kubectl get serviceaccounts
+  ```
+
+]
+
+---
+
+## Binding a role to the service account
+
+- Binding a role = creating a *rolebinding* object
+
+- We will call that object `viewercanview`
+
+  (but again, we could call it `view`)
+
+.exercise[
+
+- Create the new role binding:
+  ```bash
+  kubectl create rolebinding viewercanview \
+          --clusterrole=view \
+          --serviceaccount=default:viewer
+  ```
+
+]
+
+It's important to note a couple of details in these flags ...
+
+---
+
+## Roles vs Cluster Roles
+
+- We used `--clusterrole=view`
+
+- What would have happened if we had used `--role=view`?
+
+  - we would have bound the role `view` from the local namespace
+    <br/>(instead of the cluster role `view`)
+
+  - the command would have worked fine (no error)
+
+  - but later, our API requests would have been denied
+
+- This is a deliberate design decision
+
+  (we can reference roles that don't exist, and create/update them later)
+
+---
+
+## Users vs Service Accounts
+
+- We used `--serviceaccount=default:viewer`
+
+- What would have happened if we had used `--user=default:viewer`?
+
+  - we would have bound the role to a user instead of a service account
+
+  - again, the command would have worked fine (no error)
+
+  - ... but our API requests would have been denied later
+
+- What's about the `default:` prefix?
+
+  - that's the namespace of the service account
+
+  - yes, it could be inferred from context, but ... `kubectl` requires it
+
+---
+
+## Testing
+
+- We will run an `alpine` pod and install `kubectl` there
+
+.exercise[
+
+- Run a one-time pod:
+  ```bash
+  kubectl run eyepod --rm -ti --restart=Never \
+          --serviceaccount=viewer \
+          --image alpine
+  ```
+
+- Install `curl`, then use it to install `kubectl`:
+  ```bash
+  apk add --no-cache curl
+  URLBASE=https://storage.googleapis.com/kubernetes-release/release
+  KUBEVER=$(curl -s $URLBASE/stable.txt)
+  curl -LO $URLBASE/$KUBEVER/bin/linux/amd64/kubectl
+  chmod +x kubectl
+  ```
+
+]
+
+---
+
+## Running `kubectl` in the pod
+
+- We'll try to use our `view` permissions, then to create an object
+
+.exercise[
+
+- Check that we can, indeed, view things:
+  ```bash
+  ./kubectl get all
+  ```
+
+- But that we can't create things:
+  ```bash
+  ./kubectl run tryme --image=nginx
+  ```
+
+]
--- a/slides/new-content.yml
+++ b/slides/new-content.yml
@@ -26,16 +26,7 @@ chapters:
    explain install/remove

    in action with PostgreSQL
- - |
-    # RBAC
-
-    explain roles and systemaccounts and bindings
-
-    run kubectl in a pod with a view systemaccount
-
-    putting it together with namespaces
-
-    generate namespace + systemaccount for the namespace (for deployment)
+- - k8s/authn-authz.md
  - |
    # Ingress