Quickstart

This documentation is for a previous version of Cerbos. Choose 0.53.0 from the version picker at the top right or navigate to https://docs.cerbos.dev for the latest version.

Create a directory to store the policies.

mkdir -p cerbos-quickstart/policies

Now start the Cerbos server. We are using the container image in this guide but you can follow along using the binary as well. See installation instructions for more information.

docker run --rm --name cerbos -d -v $(pwd)/cerbos-quickstart/policies:/policies -p 3592:3592 -p 3593:3593  ghcr.io/cerbos/cerbos:0.52.0

Time to try out a simple request.

If you prefer to use Postman, Insomnia or any other software that supports OpenAPI, you can follow this guide along on those tools by downloading the OpenAPI definitions from http://localhost:3592/schema/swagger.json. You can also use the built-in API browser by pointing your browser to http://localhost:3592.

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cat <<EOF | curl --silent "http://localhost:3592/api/check/resources?pretty" -d @-
{
  "requestId": "quickstart",
  "principal": {
    "id": "bugs_bunny",
    "roles": [\
      "user"\\n    ],
    "attr": {
      "beta_tester": true
    }
  },
  "resources": [\
    {\
      "actions": [\
        "view:public",\
        "comment"\
      ],\
      "resource": {\
        "kind": "album:object",\
        "id": "BUGS001",\
        "attr": {\
          "owner": "bugs_bunny",\
          "public": false,\
          "flagged": false\
        }\
      }\
    },\
    {\
      "actions": [\
        "view:public",\
        "comment"\
      ],\
      "resource": {\
        "kind": "album:object",\
        "id": "DAFFY002",\
        "attr": {\
          "owner": "daffy_duck",\
          "public": true,\
          "flagged": false\
        }\
      }\
    }\
  ]
}
EOF

{
  "requestId": "quickstart",
  "results": [\
    {\
      "resource": {\
        "id": "BUGS001",\
        "kind": "album:object"\
      },\
      "actions": {\
        "comment": "EFFECT_DENY",\
        "view:public": "EFFECT_DENY"\
      }\
    },\
    {\
      "resource": {\
        "id": "DAFFY002",\
        "kind": "album:object"\
      },\
      "actions": {\
        "comment": "EFFECT_DENY",\
        "view:public": "EFFECT_DENY"\
      }\
    }\
  ]
}

Bugs Bunny is not allowed to view or comment on any of the album resources — even the ones that belong to him. This is because currently there are no policies defined for the album:object resource.

Now create a derived roles definition that assigns the owner dynamic role to a user if the owner attribute of the resource they’re trying to access is equal to their ID.

cat > cerbos-quickstart/policies/derived_roles_common.yaml <<EOF
---
apiVersion: "api.cerbos.dev/v1"
derivedRoles:
  name: common_roles
  definitions:
    - name: owner
      parentRoles: ["user"]
      condition:
        match:
          expr: request.resource.attr.owner == request.principal.id
EOF

Each Cerbos policy must be in its own file. You cannot define multiple policies in a single YAML or JSON file.

Also create a resource policy that gives owners full access to their own albums.

cat > cerbos-quickstart/policies/resource_album.yaml <<EOF
---
apiVersion: api.cerbos.dev/v1
resourcePolicy:
  version: "default"
  importDerivedRoles:
    - common_roles
  resource: "album:object"
  rules:
    - actions: ['*']
      effect: EFFECT_ALLOW
      derivedRoles:
        - owner
EOF

Try the request again. This time bugs_bunny should be allowed access to his own album but denied access to the album owned by daffy_duck.

{
  "requestId": "quickstart",
  "results": [\
    {\
      "resource": {\
        "id": "BUGS001",\
        "kind": "album:object"\
      },\
      "actions": {\
        "comment": "EFFECT_ALLOW",\
        "view:public": "EFFECT_ALLOW"\
      }\
    },\
    {\
      "resource": {\
        "id": "DAFFY002",\
        "kind": "album:object"\
      },\
      "actions": {\
        "comment": "EFFECT_DENY",\
        "view:public": "EFFECT_DENY"\
      }\
    }\
  ]
}

Now add a rule to the policy to allow users to view public albums.

cat > cerbos-quickstart/policies/resource_album.yaml <<EOF
---
apiVersion: api.cerbos.dev/v1
resourcePolicy:
  version: "default"
  importDerivedRoles:
    - common_roles
  resource: "album:object"
  rules:
    - actions: ['*']
      effect: EFFECT_ALLOW
      derivedRoles:
        - owner

- actions: ['view:public']
      effect: EFFECT_ALLOW
      roles:
        - user
      condition:
        match:
          expr: request.resource.attr.public == true
EOF

If you try the request again, bugs_bunny now has view:public access to the album owned by daffy_duck but not comment access. Can you figure out how to update the policy to give him comment access as well?