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Node.js / Express.js SDK

Aserto 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.

Overview#

This package provides three 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.

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

Installation#

Using npm:

npm install express-jwt-aserto

Using yarn:

yarn add express-jwt-aserto
note

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

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('express-jwt-aserto');
const options = {  authorizerServiceUrl: 'https://localhost:8383', // required - must pass a valid URL  policyId: 'policy-id-guid', // required - GUID representing policy ID  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, policyId, policyRoot } as well as authorizerApiKey and tenantId for the hosted authorizer
  • 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: URL of authorizer service (required)
  • policyId: Policy ID (required)
  • policyRoot: Policy root (required)
  • authorizerApiKey: API key for authorizer service (required if using hosted authorizer)
  • tenantId: Aserto tenant ID (required if using hosted authorizer)
  • authorizerCertFile: location on the filesystem of the CA certificate that signed the Aserto 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, Aserto 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#

The displayStateMap middleware is how the Express.js SDK exposes the display state map pattern to front-ends (e.g. the React SDK and JavaScript SPA SDK).

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('express-jwt-aserto');
const options = {  authorizerServiceUrl: 'https://localhost:8383', // required - must pass a valid URL  policyId: 'policy-id-guid', // required - GUID representing policy ID  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: URL of authorizer service (required)
  • policyId: Policy ID (required)
  • policyRoot: Policy root (required)
  • authorizerApiKey: API key for authorizer service (required if using hosted authorizer)
  • tenantId: Aserto tenant ID (required if using hosted authorizer)
  • authorizerCertFile: location on the filesystem of the CA certificate that signed the Aserto 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 Aserto 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('express-jwt-aserto');
const options = {  authorizerServiceUrl: 'https://localhost:8383', // required - must pass a valid URL  policyId: 'policy-id-guid', // required - GUID representing policy ID  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, policyId } as well as authorizerApiKey and tenantId for the hosted authorizer (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: URL of authorizer service (required)
  • policyId: Policy ID (required)
  • policyRoot: Policy root (required)
  • authorizerApiKey: API key for authorizer service (required if using hosted authorizer)
  • tenantId: Aserto tenant ID (required if using hosted authorizer)
  • authorizerCertFile: location on the filesystem of the CA certificate that signed the Aserto 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, Aserto 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 Aserto authorizer exposes HTTPS-only endpoints. In order for a Node.js policy to properly communicate with the authorizer, TLS certificates must be verified.

For a hosted authorizer that has a TLS certificate that is signed by a trusted Certificate Authority, this section isn't relevant because that TLS certificate will be successfully validated.

In a development environment, the Aserto OneBox automatically creates a set of self-signed certificates and certificates of the CA (certificate authority) that signed them. It places them in a well-known location on the filesystem, defaulting to $HOME/.config/aserto/aserto-one/certs/.

In order for the express-jwt-aserto package to perform the TLS handshake, it needs to verify the TLS certificate of the one-box using the certificate of the CA that signed it - which was placed in $HOME/.config/aserto/aserto-one/certs/aserto-one-gateway-ca.crt. Therefore, in order for this middleware to work successfully, either the authorizerCertFile 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 express-jwt-aserto 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 authorizerCertFile 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.