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Node.js / Express.js SDK

Topaz authorization middleware for the node Express server, based on Auth0's express-jwt-authz package.

GitHub​

This SDK is open source and can be found on GitHub.

This package provides four capabilities:

  1. jwtAuthz: middleware that sits on a route, and validates a request to authorize access to that route.
  2. displayStateMap: middleware that adds an endpoint for returning the display state map for a service, based on its authorization policy.
  3. is: a function that can be called to make a decision about a user's access to a resource based on a policy.
  4. ds: an object containing the object and relation functions, which can be called to retrieve an object or relation, respectively, from the directory.

The first three capabilities call out to an authorizer service, which must be configured as part of the options map passed in.

The fourth calls out to a directory service.

Installation​

Using npm:

npm install @aserto/aserto-node

Using yarn:

yarn add @aserto/aserto-node
note

express@^4.0.0 is a peer dependency. Make sure it is installed in your project.

Usage​

Note: the authorizerServiceUrl option that is used throughout is no longer a URL, but the option name is retained for backward-compatibility. It is now expected to be a hostname that exposes a gRPC binding. Any "https://" prefix is stripped out of the value provided.

jwtAuthz middleware​

jwtAuthz is an Express-compatible middleware that you can place in the dispatch pipeline of a route.

You can use the jwtAuthz function together with express-jwt to both validate a JWT and make sure it has the correct permissions to call an endpoint.

const jwt = require('express-jwt');
const { jwtAuthz } = require('aserto-node');

const options = {
  authorizerServiceUrl: 'localhost:8282', // required - must pass a valid host:port
  policyRoot: 'mycars' // required - must be a string representing the policy root (the first component of the policy module name)
};

app.get('/users/:id',
  jwt({ secret: 'shared_secret' }),
  jwtAuthz(options),
  function(req, res) { ... });

By default, jwtAuthz derives the policy file name and resource key from the Express route path. To override this behavior, two optional parameters are available.

arguments​

jwtAuthz(options[, packageName[, resourceMap]]):

  • options: a javascript map containing at least { authorizerServiceUrl, policyRoot, authorizerCertCAFile }
  • packageName: a string representing the policy package name (optional)
  • resourceMap: a map of key/value pairs to use as the resource context for evaluation (optional)

options argument​

  • authorizerServiceUrl: hostname:port of authorizer service (required)
  • policyRoot: Policy root (required)
  • authorizerCertCAFile: location on the filesystem of the CA certificate that signed the Topaz authorizer self-signed certificate. See the "Certificates" section for more information.
  • disableTlsValidation: ignore TLS certificate validation when creating a TLS connection to the authorizer. Defaults to false.
  • failWithError: When set to true, will forward errors to next instead of ending the response directly.
  • useAuthorizationHeader: When set to true, will forward the Authorization header to the authorizer. The authorizer will crack open the JWT and use that as the identity context. Defaults to true.
  • identityHeader: the name of the header from which to extract the identity field to pass into the authorize call. This only happens if useAuthorizationHeader is false. Defaults to 'identity'.
  • customUserKey: The property name to check for the subject key. By default, permissions are checked against req.user, but you can change it to be req.myCustomUserKey with this option. Defaults to user.
  • customSubjectKey: The property name to check for the subject. By default, permissions are checked against user.sub, but you can change it to be user.myCustomSubjectKey with this option. Defaults to sub.

packageName argument​

By convention, Topaz policy package names are of the form policyRoot.METHOD.path. By default, the package name will be inferred from the policy name, HTTP method, and route path:

  • GET /api/users --> policyRoot.GET.api.users
  • POST /api/users/:id --> policyRoot.POST.api.users.__id

Passing in the packageName parameter into the jwtAuthz() function will override this behavior.

resourceMap argument​

By default, the resource map will be req.params. For example, if the route path is /api/users/:id, the resource will be { 'id': 'value-of-id' }.

Passing in the resourceMap parameter into the jwtAuthz() function will override this behavior.

displayStateMap middleware​

Use the displayStateMap middleware to set up an endpoint that returns the display state map to a caller. The endpoint is named __displaystatemap by default, but can be overridden in options.

const { displayStateMap } = require('aserto-node');

const options = {
  authorizerServiceUrl: 'localhost:8282', // required - must pass a valid host:port
  policyRoot: 'policy' // required - must be a string representing the policy root (the first component of the policy module name)
};
app.use(displayStateMap(options));

arguments​

displayStateMap(options)

options argument​

  • authorizerServiceUrl: hostname:port of authorizer service (required)
  • policyRoot: Policy root (required)
  • authorizerCertCAFile: location on the filesystem of the CA certificate that signed the Topaz authorizer self-signed certificate. See the "Certificates" section for more information.
  • disableTlsValidation: ignore TLS certificate validation when creating a TLS connection to the authorizer. Defaults to false.
  • endpointPath: display state map endpoint path, defaults to /__displaystatemap.
  • failWithError: When set to true, will forward errors to next instead of ending the response directly. Defaults to false.
  • useAuthorizationHeader: When set to true, will forward the Authorization header to the authorizer. The authorizer will crack open the JWT and use that as the identity context. Defaults to true.
  • identityHeader: the name of the header from which to extract the identity field to pass into the displayStateMap call. This only happens if useAuthorizationHeader is false. Defaults to 'identity'.
  • customUserKey: The property name to check for the subject key. By default, permissions are checked against req.user, but you can change it to be req.myCustomUserKey with this option. Defaults to user.
  • customSubjectKey: The property name to check for the subject. By default, permissions are checked against user.sub, but you can change it to be user.myCustomSubjectKey with this option. Defaults to sub.

'is' function​

While jwtAuthz is meant to be used as dispatch middleware for a route, is provides an explicit mechanism for calling the Topaz authorizer.

Use the is function to call the authorizer with a decision, policy, and resource, and get a boolean true or false response. The decision is a named value in the policy: the string allowed is used by convention. Examples: is('allowed'), is('enabled'), is('visible'), etc.

const { is } = require('aserto-node');

const options = {
  authorizerServiceUrl: 'localhost:8282', // required - must pass a valid host:port
  policyRoot: 'policy' // required - must be a string representing the policy root (the first component of the policy module name)
};

app.get('/users/:id', async function(req, res) {
  try {
    const allowed = await is('allowed', req, options);
    if (allowed) {
      ...
    } else {
      res.status(403).send("Unauthorized");
    }
  } catch (e) {
    res.status(500).send(e.message);
  }
});

arguments​

is(decision, req, options[, packageName[, resourceMap]]):

  • decision: a string representing the name of the decision - typically allowed (required)
  • req: Express request object (required)
  • options: a javascript map containing at least { authorizerServiceUrl, policyRoot, authorizerCertCAFile } (required)
  • packageName: a string representing the package name for the the policy (optional)
  • resourceMap: a map of key/value pairs to use as the resource context for evaluation (optional)

decision argument​

This is simply a string that is correlates to a decision referenced in the policy: for example, allowed, enabled, etc.

req argument​

The Express request object.

options argument​

  • authorizerServiceUrl: hostname:port of authorizer service (required)
  • policyRoot: Policy root (required)
  • authorizerCertCAFile: location on the filesystem of the CA certificate that signed the Topaz authorizer self-signed certificate. See the "Certificates" section for more information.
  • disableTlsValidation: ignore TLS certificate validation when creating a TLS connection to the authorizer. Defaults to false.
  • useAuthorizationHeader: When set to true, will forward the Authorization header to the authorizer. The authorizer will crack open the JWT and use that as the identity context. Defaults to true.
  • identityHeader: the name of the header from which to extract the identity field to pass into the authorize call. This only happens if useAuthorizationHeader is false. Defaults to 'identity'.
  • customUserKey: The property name to check for the subject key. By default, permissions are checked against req.user, but you can change it to be req.myCustomUserKey with this option. Defaults to user.
  • customSubjectKey: The property name to check for the subject. By default, permissions are checked against user.sub, but you can change it to be user.myCustomSubjectKey with this option. Defaults to sub.

packageName argument​

By default, is will follow the same heuristic behavior as jwtAuthz - it will infer the packge name from the policy name, HTTP method, and route path. If provided, the packageName argument will override this and specify a policy package to use.

By convention, Topaz Rego policies are named in the form policyRoot.METHOD.path. Following the node.js idiom, you can also pass it in as policyRoot/METHOD/path, and the path can contain the Express parameter syntax.

For example, passing in policyRoot/GET/api/users/:id will resolve to a policy called policyRoot.GET.api.users.__id.

resourceMap argument​

By default, is follows the same behavior as jwtAuthz in that resource map will be req.params. For example, if the route path is /api/users/:id, the resource will be { 'id': 'value-of-id' }.

Passing in the resourceMap parameter into the is() function will override this behavior.

Certificates​

The Topaz authorizer exposes SSL-only endpoints. In order for a Node.js policy to properly communicate with the authorizer, TLS certificates must be verified.

In order for the aserto-node package to perform the TLS handshake, it needs to verify the TLS certificate of the Topaz authorizer using the certificate of the CA that signed it - which was placed in $HOME/.config/topaz/certs/grpc-ca.crt. Therefore, in order for this middleware to work successfully, either the authorizerCertCAFile must be set to the correct path for the CA cert file, or the disableTlsValidation flag must be set to true.

Furthermore, when packaging a policy for deployment (e.g. in a Docker container) which uses aserto-node to communicate with an authorizer that has a self-signed TLS certificate, you must copy this CA certificate into the container as part of the Docker build (typically performed in the Dockerfile). When you do that, you'll need to override the authorizerCertCAFile option that is passed into any of the API calls defined above with the location of this cert file.

Alternately, to ignore TLS certificate validation when creating a TLS connection to the authorizer, you can set the disableTlsValidation option to true and avoid TLS certificate validation. This option is not recommended for production.

Directory​

The Directory APIs can be used to get or set object instances and relation instances. They can also be used to check whether a user has a permission or relation on an object instance.

Directory Client​

You can initialize a directory client as follows:

import { ds } from "@aserto/aserto-node";

const directoryClient = ds({
  url: 'localhost:9292',
  tenantId: '1234',
  apiKey: 'my-api-key',
});

- `url`: hostname:port of directory service (_required_)
- `apiKey`: API key for directory service (_required_ if using hosted directory)
- `tenantId`: Aserto tenant ID (_required_ if using hosted directory)
- `rejectUnauthorized`: reject clients with invalid certificates. Defaults to `true`.

Getting objects and relations​

'object' function​

object({ type: "type-name", key: "object-key" }):

Get an object instance with the type type-name and the key object-key. For example:

const user = await directoryClient.object({ type: 'user', key: 'euang@acmecorp.com' });

'relation' function​

  relation({
    subject: {
      type: 'subject-type',
    },
    object: {
      type: 'object-type',
      key: 'object-key'
    },
    relation: {
      name: 'relation-name',
      objectType: 'object-type'
    }
  })

Get an array of relations of a certain type for an object instance. For example:

const identity = 'euang@acmecorp.com';
const relations = await directoryClient.relation(
  {
    subject: {
      type: 'user',
    },
    object: {
      type: 'identity',
      key: identity
    },
    relation: {
      name: 'identifier',
      objectType: 'identity'
    }
  }
);

Setting objects and relations​

'setObject' function​

setObject({ object: $Object }):

Create an object instance with the specified fields. For example:

user = directoryClient.setObject(
  {
    object: {
      type: "user",
      key: "test-object",
      properties: {
        displayName: "test object"
      }
    }
  }
);

'setRelation' function​

setRelation({ subject: ObjectIdentifier, relation: String, object: ObjectIdentifier }):

Create a relation with a specified name between two objects. For example:

const relation = await directoryClient.setRelation(
  {
    subject: {
      key: 'subjectKey',
      type: 'subjectType',
    },
    relation: 'relationName',
    object: {
      type: 'objectType',
      key: 'objectKey',
    },
  }
);

'deleteObject' function​

deleteObject({ type: "type-name", key: "object-key" }):

Deletes an object instance with the specified type and key. For example:

await directoryClient.deleteObject({ type: 'user', key: 'euang@acmecorp.com' });

'deleteRelation' function​

deleteRelation({ subject: ObjectIdentifier, relation: RelationIdentifier, object: ObjectIdentifier }):

Delete a relation:

await directoryClient.deleteRelation(
  {
    subject: {
      key: 'subjectKey',
      type: 'subjectType',
    },
    relation: {
      name: 'relationName',
      object_type: 'objectType',
    },
    object: {
      type: 'objectType',
      key: 'objectKey',
    },
  }
);

Checking permissions and relations​

You can evaluate graph queries over the directory, to determine whether a subject (e.g. user) has a permission or a relation to an object instance.

'checkPermission' function​

checkPermission({ subject: ObjectIdentifier, permission: PermissionIdentifier, object: ObjectIdentifier }):

Check that an user object with the key euang@acmecorp.com has the read permission in the admin group:

const check = await directoryClient.checkPermission(
  {
    subject: {
      key: 'euang@acmecorp.com',
      type: 'user',
    },
    permission: {
      name: 'read',
    },
    object: {
      type: 'group',
      key: 'admin',
    },
  }
);

'checkRelation' function​

checkPermission({ subject: ObjectIdentifier, permission: PermissionIdentifier, object: ObjectIdentifier }):

Check that euang@acmecorp.com has an identifier relation to an object with key euang@acmecorp.com and type identity:

const check = directoryClient.checkPermission(
  {
    subject: {
      key: 'euang@acmecorp.com',
      type: 'user',
    },
    relation: {
       name: "identifier",
       object_type: "identity"
      },
    object: {
      type: 'identity',
      key: 'euang@acmecorp.com',
    },
  }
);

Example​

const identity = 'euang@acmecorp.com';
const relation = await directoryClient.relation(
  {
    subject: {
      type: 'user',
    },
    object: {
      type: 'identity',
      key: identity
    },
    relation: {
      name: 'identifier',
      objectType: 'identity'
    }
  }
);

if (!relation || relation.length === 0) {
  throw new Error(`No relations found for identity ${identity}`, )
};

const user = await directoryClient.object(relation[0].subject);