Authorization

The NATS server supports authorization using subject-level permissions on a per-user basis. Permission-based authorization is available with multi-user authentication via the users list.

Each permission specifies the subjects the user can publish to and subscribe to. The parser is generous at understanding what the intent is, so both arrays and singletons are processed. For more complex configuration, you can specify a permission object which explicitly allows or denies subjects. The specified subjects can specify wildcards as well. Permissions can make use of variables.

A special field inside the authorization map is default_permissions. When present, it contains permissions that apply to users that do not have permissions associated with them.

Permissions Configuration Map

The permissions map specify subjects that can be subscribed to or published by the specified client.

Permission Map

The permission map provides additional properties for configuring a permissions map. Instead of providing a list of allowable subjects and optional queues, the permission map allows you to explicitly list those you want toallow or deny. Both lists can be provided. In case of overlap deny has priority.

Important Note It is important to not break request-reply patterns. In some cases (as shown below) you need to add rules for the _INBOX.> pattern. If an unauthorized client publishes or attempts to subscribe to a subject that has not been allow listed, the action fails and is logged at the server, and an error message is returned to the client. The allow responses option can simplify this.

Allow Responses Map

The allow_responses option dynamically allows publishing to reply subjects and is designed for service responders. When set to true, an implicit publish allow permission is enforced which enables the service to have temporary permission to publish to the reply subject during a request-reply exchange. If true, the client supports a one-time publish. If allow_responses is a map, it allows you to configure a maximum number of responses and how long the permission is valid.

{% hint style=”danger” %} Note, when allow_responses is enabled, the reply subject is not constrained to the publish allow or deny list. The implication of this is that a reply subject can be provided by a client to a service (responder) that does not have permission to explicitly publish on that subject, but is temporarily allowed given this option. If explicit control over which subjects a client is allowed to reply to, do not use allow_responses and instead define allow/deny lists under the publish permission map. {% endhint %}

When allow_responses is set to true, it defaults to the equivalent of { max: 1 } and no time limit.

Important Note When using nsc to configure your users, you can specify the --allow-pub-response and --response-ttl to control these settings.

Examples

Variables

Here is an example authorization configuration that uses variables which defines four users, three of whom are assigned explicit permissions.

authorization {
  default_permissions = {
    publish = "SANDBOX.*"
    subscribe = ["PUBLIC.>", "_INBOX.>"]
  }
  ADMIN = {
    publish = ">"
    subscribe = ">"
  }
  REQUESTOR = {
    publish = ["req.a", "req.b"]
    subscribe = "_INBOX.>"
  }
  RESPONDER = {
    subscribe = ["req.a", "req.b"]
    publish = "_INBOX.>"
  }
  users = [
    {user: admin,   password: $ADMIN_PASS, permissions: $ADMIN}
    {user: client,  password: $CLIENT_PASS, permissions: $REQUESTOR}
    {user: service,  password: $SERVICE_PASS, permissions: $RESPONDER}
    {user: other, password: $OTHER_PASS}
  ]
}

default_permissions is a special entry. If defined, it applies to all users that don’t have specific permissions set.

• admin has ADMIN permissions and can publish/subscribe on any subject. We use the wildcard > to match any subject.
• client is a REQUESTOR and can publish requests on subjects req.a or req.b, and subscribe to anything that is a response (_INBOX.>).
• service is a RESPONDER to req.a and req.b requests, so it needs to be able to subscribe to the request subjects and respond to clients that can publish requests to req.a and req.b. The reply subject is an inbox. Typically inboxes start with the prefix _INBOX. followed by a generated string. The _INBOX.> subject matches all subjects that begin with _INBOX..
• other has no permissions granted and therefore inherits the default permission set.

Note that in the above example, any client with permission to subscribe to _INBOX.> can receive all responses published. More sensitive installations will want to add or subset the prefix to further limit subjects that a client can subscribe. Alternatively, Accounts allow complete isolation limiting what members of an account can see.

Allow/Deny Specified

Here’s an example without variables, where the allow and deny options are specified:

authorization: {
    users = [
        {
            user: admin
            password: secret
            permissions: {
                publish: ">"
                subscribe: ">"
            }
        }
        {
            user: test
            password: test
            permissions: {
                publish: {
                    deny: ">"
                },
                subscribe: {
                    allow: "client.>"
                }
            }
        }
    ]
}

allow_responses

Here’s an example with allow_responses:

authorization: {
    users: [
        { user: a, password: a },
        { user: b, password: b, permissions: {subscribe: "q", allow_responses: true } },
        { user: c, password: c, permissions: {subscribe: "q", allow_responses: { max: 5, expires: "1m" } } }
        { user: d, password: d, permissions: {subscribe: "q", publish: "x", allow_responses: true } }
    ]
}

• User a has no restrictions.
• User b can listen on q for requests and can only publish once to reply subjects. All other publish subjects are denied implicitly when allow_responses is set.
• User c can listen on q for requests, but is able to return at most 5 reply messages, and the reply subject can be published at most for 1 minute.
• User d has the same behavior as user b, except that it can explicitly publish to subject x as well, which overrides the implicit deny from allow_responses.

Queue Permissions

User a can ony subscribe to foo as part of the queue subscriptions queue. User b has permissions for queue subscriptions as well as plain subscriptions. You can allow plain subscriptions on foo but constrain the queues to which a client can join, as well as preventing any service from using a queue subscription with the name *.prod:

users = [
  {
    user: "a", password: "a", permissions: {
      sub: {
        allow: ["foo queue"]
     }
  }
  {
    user: "b", password: "b", permissions: {
      sub: {
        # Allow plain subscription foo, but only v1 groups or *.dev queue groups
        allow: ["foo", "foo v1", "foo v1.>", "foo *.dev"]
        # Prevent queue subscriptions on prod groups
        deny: ["> *.prod"]
     }
  }
]