JWT-to-RBAC

JWT-to-RBAC lets you automatically generate RBAC resources based on JWT token.

Context

For authentication we use Dex with the LDAP and GitHub connectors. The users in LDAP have group memberships, GitHub users can be members of a team in an organization and Dex issues a JWT token containing these memberships. The JWT-to-RBAC project can create ServiceAccount, ClusterRoles and ClusterroleBindings based on JWT tokens. When we create a new ServiceAccount K8s automatically generates a service account token.

For more information and context please read the Provider agnostic authentication and authorization in Kubernetes post.

JWT-to-RBAC is a core part of Banzai Cloud Pipeline, a Cloud Native application and devops platform that natively supports multi- and hybrid-cloud deployments with multiple authentication backends. Check out the developer beta:

Requirements:

There are some pre-requirements to kick this of for your own testing.

• Configured Dex server as OIDC provider which issues JWT tokens. If you want to issue tokens with Dex you have to configure it with LDAP connector. You can use the Banzai Cloud Dex chart.
• GitHub account assigned for an organization or configured LDAP server - you can use the openldap Docker image
• Authentication application which uses Dex as an OpenID connector (in our case is Pipeline.

Dex acts as a shim between a client app and the upstream identity provider. The client only needs to understand OpenID Connect to query Dex.

The issued ID tokens must contain the following claims:

• name: string
• email: string
• email_verified: bool
• groups: list of strings
• federated_claims: object

federated_claims must contain:

• connector_id: string (github/ldal/local)
• user_id: string

The whole process is broken down to two main parts:

• Dex (OIDC) auth flow
• jwt-to-rbac ServiceAccount creation flow

Dex authentication flow:

1. User visits Authentication App.
2. Authentication App redirects user to Dex with an OAuth2 request.
3. Dex determines user's identity.
4. Dex redirects user to Authentication App with a code.
5. Authentication App exchanges code with Dex for an ID token.

jwt-to-rbac Flow:

1. Authentication App has ID token (JWT)
2. POST ID token to jwt-to-rbac App
3. jwt-to-rbac validates ID token with Dex or other OIDC prvider
4. jwt-to-rbac extracts username, groups and so on from the token
5. jwt-to-rbac calls API server to crate ServiceAccount, ClusterRoles and ClusterRoleBindings
6. jwt-to-rbac get service account token and sends it to Authentication App
7. Authentication App sends back the service account token to User
8. User authenticate on K8s using service account token

The ID token issued by Dex has a following content:

{
  "iss": "http://dex/dex",
  "sub": "CiNjbj1qYW5lLG91PVBlb3BsZSxkYz1leGFtcGxlLGRjPW9yZxIEbGRhcA",
  "aud": "example-app",
  "exp": 1549661603,
  "iat": 1549575203,
  "at_hash": "_L5EkeNocRsG7iuUG-pPpQ",
  "email": "[email protected]",
  "email_verified": true,
  "groups": [
    "admins",
    "developers"
  ],
  "name": "jane",
  "federated_claims": {
    "connector_id": "ldap",
    "user_id": "cn=jane,ou=People,dc=example,dc=org"
  }
}

After jwt-to-rbac extracts the information from the token, creates ServiceAccount and ClusterRoleBinding using one of the default K8s ClusterRole as roleRef or generate one defined in configuration if it does't exist.

Default K8s ClusterRoles used by jwt-to-rbac

The JWT-to-RBAC dos not create a new ClusterRole in every case; for example if a user is a member of admin group, it doesn't create this ClusterRole because K8s has already one by default.

Default ClusterRole	Description
cluster-admin	Allows super-user access to perform any action on any resource.
admin	Allows admin access, intended to be granted within a namespace using a RoleBinding.
edit	Allows read/write access to most objects in a namespace.
view	Allows read-only access to see most objects in a namespace.

jwt-to-rbac crate custom ClusterRole defined in config

In most of the cases there are different LDAP groups, so custom groups can be configured with custom rules.

[[rbachandler.customGroups]]
groupName = "developers"
[[rbachandler.customGroups.customRules]]
verbs = [
  "get",
  "list"
]
resources = [
  "deployments",
  "replicasets",
  "pods"
]
apiGroups = [
  "",
  "extensions",
  "apps"
]

define GitHub custom roles in config

[[rbachandler.customGroups]]
groupName = "githubOrg-githubTeam"
[[rbachandler.customGroups.customRules]]
verbs = [
  "get",
  "list"
]
resources = [
  "deployments",
  "replicasets",
  "pods"
]
apiGroups = [
  "",
  "extensions",
  "apps"
]

or specify GitHub organization as default org

[rbachandler]
githubOrg = "github_organization"
[[rbachandler.customGroups]]
groupName = "githubTeam"
[[rbachandler.customGroups.customRules]]
verbs = [
  "get",
  "list"
]
resources = [
  "deployments",
  "replicasets",
  "pods"
]
apiGroups = [
  "",
  "extensions",
  "apps"
]

Example configuration in yaml using default GitHub org

issued jwt:

{
  "iss": "http://dex/dex",
  "sub": "xxxxxxxxxxxxxxxxxxxxx",
  "aud": "example-app",
  "exp": 1551179050,
  "iat": 1551092650,
  "at_hash": "xxxxxxxxxxxxxxxxxxx",
  "email": "[email protected]",
  "email_verified": true,
  "groups": [
    "pokeorg",
    "pokeorg:admin",
    "pokeorg:developer"
  ],
  "name": "Peter Balogh",
  "federated_claims": {
    "connector_id": "github",
    "user_id": "13311234"
  }
}

example config:

app:
  addr: ":5555"

log:
  level: "4"
  format: "json"
  noColor: true

tokenhandler:
  oidc:
    clientID: example-app
    issuerURL: "http://dex/dex"

rbachandler:
  githubOrg: "pokeorg"
  customGroups:
  - groupName: developer
    customRules:
    - verbs: [ "get", "list" ]
      resources: [ "deployments", "replicasets", "pods" ]
      apiGroups: [ "", "extensions", "apps" ]
    namespaces: ["example_namespace"] # Only if you want to isolate the customRules to some namespaces, if you want that the customRules to apply to all namespaces delete this hole line...
  kubeConfig: "/Users/poke/.kube/config"

Define custom CA cert or set insecure connection

[tokenhandler]
caCertPath = "/path/to/tls.crt"
insecure = false

Setting insecure conection in command line:

jwt-to-rbac --tokenhandler.insecure=true

So to conclude on the open source JWT-to-RBAC project - follow these stpes if you would like to try it or check it out already in action by subscribing to our free developer beta at https://beta.banzaicloud.io/.

1. Deploy jwt-to-rbac to Kubernetes

After you cloning the GitHub repository you can compile a code and make a docker image with one command.

make docker

If you are using docker-for-desktop or minikube, you'll be able to deploy it using locally with the newly built image.

kubectl create -f deploy/rbac.yaml
kubectl create -f deploy/configmap.yaml
kubectl create -f deploy/deployment.yaml
kubectl create -f deploy/service.yaml
# port-forward locally
kubectl port-forward svc/jwt-to-rbac 5555

Now you can communicate with the jwt-to-rbac app.

2. POST ID token issued by Oidc to jwt-to-rbac API

curl --request POST \
  --url http://localhost:5555/rbac/ \
  --header 'Content-Type: application/json' \
  --data '{"token": "example.jwt.token"}'

# response:
{
    "Email": "[email protected]",
    "Groups": [
        "admins",
        "developers"
    ],
    "FederatedClaims": {
        "connector_id": "ldap",
        "user_id": "cn=jane,ou=People,dc=example,dc=org"
    }
}

The ServiceAccount, ClusterRoles (if ID token has some defined custom groups we discussed) and ClusterRoleBindings are created.

Listing the created K8s resources:

curl --request GET \
  --url http://localhost:5555/rbac \
  --header 'Content-Type: application/json'

#response:
{
    "sa_list": [
        "janedoe-example-com"
    ],
    "crole_list": [
        "developers-from-jwt"
    ],
    "crolebind_list": [
        "janedoe-example-com-admin-binding",
        "janedoe-example-com-developers-from-jwt-binding"
    ]
}

3. GET the default K8s token of ServiceAccount

curl --request GET \
  --url http://localhost:5555/tokens/janedoe-example-com \
  --header 'Content-Type: application/json'

# response:
[
    {
        "name": "janedoe-example-com-token-m4gbj",
        "data": {
            "ca.crt": "example-ca-cer-base64",
            "namespace": "ZGVmYXVsdA==",
            "token": "example-k8s-sa-token-base64"
        }
    }
]

4. Generate a ServiceAccount token with TTL

curl --request POST \
  --url http://localhost:5555/tokens/janedoe-example-com \
  --header 'Content-Type: application/json'
  --data '{"duration": "12h30m"}'

# response:
[
    {
        "name": "janedoe-example-com-token-df3re",
        "data": {
            "ca.crt": "example-ca-cer-base64",
            "namespace": "ZGVmYXVsdA==",
            "token": "example-k8s-sa-token-with-ttl-base64"
        }
    }
]

Now you have a base64 encoded service account token.

5. Accessing with ServiceAccount token

You can use service account token from command line:

kubectl --token $TOKEN_TEST --server $APISERVER get po

Or create kubectl context with it:

export TOKEN=$(echo "example-k8s-sa-token-base64" | base64 -D)
kubectl config set-credentials "janedoe-example-com" --token=$TOKEN
# with kubectl config get-clusters you can get cluster name
kubectl config set-context "janedoe-example-com-context" --cluster="clustername" --user="janedoe-example-com" --namespace=default
kubectl config use-context janedoe-example-com-context
kubectl get pod

As a final note - since we use Dex, which is an identity service that uses OpenID Connect to drive authentication for other apps, any other supported connector can be used for authentication to Kubernetes.