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nats-iam-broker*

*for the Decentralised Auth Callout flow

A configurable NATS micro-service that exchanges Identity Provider (IdP) tokens1 for NATS user authorization JWTs. This component helps implement the decentralised auth callout flow:

  1. A prospective NATS user authenticates with their IdP, and passes the obtained token to NATS.
  2. This micro-service (re-)validates the IdP token.
  3. This micro-service mints a new NATS user access token with specific authorizations.

1https://www.iana.org/assignments/jwt/jwt.xhtml

What does it do?

The assumption is that implementations of auth callout microservices are almost identical, but for the process of determining which authorizations should be assigned to the minted NATS user access tokens.

This component implements the boilerplate code and using YAML configuration and golang templating, allows construction of JWTs with claims of the form:

claims(NATS_JWT) = f(claims(idpJwt))

where:

  • f is a function that extracts and transforms claims from the IdP's Jwt.
  • idpClaims is the IdP JWT supplied from the user.

Examples

The mock OIDC/OAuth2 service https://oidctest.wsweet.org/ is used to obtain an authenticated JWT id_token.

The example scripts in the scripts/ and examples/ folders demonstrate how to configure, deploy and test this micro-service. These are structred as:

  • scripts
  • examples
    • /<example_name>
      • /<name>_initial_setup.sh, one-time script to setup decentralised accounts and users
      • /<name>_start_service.sh, configures and starts the auth callout micro-service
      • /<name>_simulate_login.sh, contacts IdP, authenticates, and uses the obtained token to establish a client connection with NATS
      • /run.sh, run all steps in the example

Assuming docker is installed, the examples can be run using: make example-<example_name>.

Example 1: RGB.org

The RGB.org organisation has three departments that share a single NATS deployment. A department consists of several teams, with each team developing a set of applications.

The blue department has this setup.

  • there are three teams: App Team 1, App Team 2, App Team 3

    • they have each developed apps that require access to NATS.
    • users of App Teami's apps have NATS credentials minted by NATS account APPi

  • the department has configured and deployed a shared instance of the nats-iam-broker microservice.

    • the microservice connects to NATS using user minter of NATS account MINT_11.
    • minting accounts have an additional user nobody, that has no permissions.

Bob is a member of App Team 3, and wishes to use their in-house app demo-app. This section describes the authentication and authorization flow.

  1. Bob launches demo-app.

    • demo-app directs him to OIDC Provider2 for authentication, which Bob completes.
    • demo-app receives back a signed JWT token jwt.provider2.bob.

  2. demo-app obtains credentials1 for MINT_11(nobody) and packages this into a NATS authorization_request (perhaps by calling nats.connect())2.

  3. NATS creates a connection_id for the Bob's instance of demo-app, and directs the MINT_11(nobody) connection to the blue department's nats-iam-broker microservice. This is because the microservice connects to NATS using MINT_11(minter), and the two have a common NATS account. The connection between NATS and nats-iam-broker is private3.

  4. nats-iam-broker microservice receives the request.

    • it unpacks jwt.provider2.bob and validates the token against OIDC Provider2.
    • it performs additional validations, like checking JWT expiry/clock skew, etc.
    • an unsuccessful validation reports an Authorization Violation back to the user.

  5. nats-iam-broker microservice mints a new JWT.

    • it inspects Bob's user/profile information in jwt.provider2.bob.
    • it determines that the account to issue+sign the minted token is APP3.
    • it creates a set of unique authorizations for Bob's demo-app usage.
    • it sets a suitable token expiry etc.

  6. nats-iam-broker signs the minted JWT, encrypts it for transport and sends it to NATS server.

  7. NATS server decrypts3 and validates the nats-jwt, and binds the authorizations to the client's connection_id. Finally, it notifies Bob's instance of demo-app of the successful connection.

1 although nobody user credentials have no NATS permissions, storing them externally can facilitate key rotation of signing_key(MINT_11).

2 a (somewhat) arbitrary decision has been made to pass the third-party JWT in the password field, i.e., nats.Connect(UserCredentials(MINT_11(nobody)), password=jwt.provider2.bob)

3 this uses the XKey field. It is optional but recommended.

Example 2: Basic

This example demonstates a simpler setup consisting of:

  • one auth callout microservice MINT, with standard users minter and nobody
  • one appliction account APP1

As in the previous example, authorised NATS users are created and signed on-the-fly, following successful validation of the IdP token.

Setup

The application is intended to be deployed as either:

Standard go templating is used to construct roles dynamically. Templating functions are listed in the filters module.

The configuration structure is outlined here.

Key Type Description
nats.url string NATS server URL
service.name string name of deployed micro-service instance
service.version string version of deployed micro-service instance
service.description string description of deployed micro-service instance
service.creds_file string user credentials used to connect to NATS
service.account.name string (metadata) human-readable reminder of account used to sign and encrypt communications with NATS server
service.account.signing_nkey string key used to sign new user-jwt returned to NATS
service.account.encryption.enabled bool toggle for communication-encryption with NATS server
service.account.encryption.xkey_secret string trusted secret-key for encryption with NATS server
nats_jwt.exp_max duration maximum duration of minted nats user-jwt
idp.client_id string the client identifier registered with the IdP
idp.issuer_url string the url of the IdP issuer
idp.validation.claims []string set of required claims on idp token
idp.validation.aud []string set of allowed values for audience claim
idp.validation.exp.min duration minimum time to expiry for idp token from now
idp.validation.exp.max duration maximum duration of idp token from now
rbac.user_accounts - set of accounts configured to issue and sign nats user-jwts
rbac.user_accounts[i].name string name of user-jwt signing account
rbac.user_accounts[i].public_key string public key of user-jwt signing account
rbac.user_accounts[i].signing_nkey string signing key of user-jwt signing account in nkey format
rbac.roles - set of referenceable nats jwt permission groupings
rbac.roles[i].name string role name
rbac.roles[i].permissions jwt.Permissions nats-io/jwt permissions structure (see link)
rbac.roles[i].limits jwt.Limits nats-io/jwt limits structure (see link)
rbac.role_binding[i].user_account string user account to bind
rbac.role_binding[i].roles []string set of roles to bind
rbac.role_binding[i].match.claim string name of IdP JWT claim to match on
rbac.role_binding[i].match.value string corresponding value of IdP JWT claim to match on

References

  1. youtube, synadia auth-callout: https://www.youtube.com/watch?v=VvGxrT-jv64
  2. youtube: synaida decentralised auth callout: https://www.youtube.com/watch?v=5pQVjN0ym5w
  3. natsbyexample: https://natsbyexample.com/examples/auth/callout-decentralized/cli
  4. rethinking connectivity 19: https://github.com/synadia-io/rethink_connectivity/tree/main/19-auth-callout
  5. mock oidc service: https://lemonldap-ng.org/documentation/latest/testopenidconnect.html