HMAC Authentication

Add HMAC Signature authentication to a Service or a Route to establish the integrity of incoming requests. The plugin will validate the digital signature sent in the Proxy-Authorization or Authorization header (in this order). This plugin implementation is based off the draft-cavage-http-signatures draft with a slightly different signature scheme.

Configuration Reference

This plugin is partially compatible with DB-less mode.

In DB-less mode, you configure Kong Gateway declaratively. Therefore, the Admin API is mostly read-only. The only tasks it can perform are all related to handling the declarative config, including:

• Setting a target's health status in the load balancer
• Validating configurations against schemas
• Uploading the declarative configuration using the /config endpoint

Consumers and Credentials can be created with declarative configuration.

Admin API endpoints which do POST, PUT, PATCH or DELETE on Credentials will not work on DB-less mode.

Example plugin configuration

curl -X POST http://localhost:8001/services/SERVICE_NAME|SERVICE_ID/plugins \
    --data "name=hmac-auth" 

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: hmac-auth-example
config:
  EXAMPLE_PARAMETER: EXAMPLE_VALUE
plugin: hmac-auth

apiVersion: v1
kind: Service
metadata:
  name: SERVICE_NAME|SERVICE_ID
  labels:
    app: SERVICE_NAME|SERVICE_ID
  annotations:
    konghq.com/plugins: hmac-auth-example
spec:
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: SERVICE_NAME|SERVICE_ID
  selector:
    app: SERVICE_NAME|SERVICE_ID

plugins:
- name: hmac-auth
  service: SERVICE_NAME|SERVICE_ID
  config:
    EXAMPLE_PARAMETER: EXAMPLE_VALUE

$ curl -X POST http://localhost:8001/routes/ROUTE_NAME|ROUTE_ID/plugins \
    --data "name=hmac-auth" 

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: hmac-auth-example
config:
  EXAMPLE_PARAMETER: EXAMPLE_VALUE
plugin: hmac-auth

apiVersion: networking/v1beta1
kind: Ingress
metadata:
  name: ROUTE_NAME|ROUTE_ID
  annotations:
    kubernetes.io/ingress.class: kong
    konghq.com/plugins: hmac-auth-example
spec:
  rules:
  - host: examplehostname.com
    http:
      paths:
      - path: /bar
        backend:
          serviceName: echo
          servicePort: 80

plugins:
- name: hmac-auth
  route: ROUTE_NAME
  config:
    EXAMPLE_PARAMETER: EXAMPLE_VALUE

$ curl -X POST http://localhost:8001/plugins/ \
    --data "name=hmac-auth" 

apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: <global-hmac-auth>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config:
  <optional_parameter>: <value>
plugin: hmac-auth

plugins:
- name: hmac-auth
  config:
    EXAMPLE_PARAMETER: EXAMPLE_VALUE

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

Once applied, any user with a valid credential can access the Service/Route. To restrict usage to only some of the authenticated users, also add the ACL plugin (not covered here) and create whitelist or blacklist groups of users.

Usage

In order to use the plugin, you first need to create a Consumer to associate one or more credentials to.

Note: Because the HMAC signature is generated by the client, you should make sure that Kong does not update or remove any request parameter used in HMAC signature before this plugin runs.

Create a Consumer

You need to associate a credential to an existing Consumer object. A Consumer can have many credentials.

curl -d "username=user123&custom_id=SOME_CUSTOM_ID" http://kong:8001/consumers/

consumers:
- username: user123
  custom_id: SOME_CUSTOM_ID

In both cases, the parameters are as described below:

Create a Credential

$ curl -X POST http://kong:8001/consumers/{consumer}/hmac-auth \
    --data "username=bob" \
    --data "secret=secret456"

hmacauth_credentials:
- consumer: {consumer}
  username: bob
  secret: secret456

In both cases the fields/parameters work as follows:

Signature Authentication Scheme

The client is expected to send an Authorization or Proxy-Authorization header with the following parameterization:

credentials := "hmac" params
params := keyId "," algorithm ", " headers ", " signature
keyId := "username" "=" plain-string
algorithm := "algorithm" "=" DQUOTE (hmac-sha1|hmac-sha256|hmac-sha384|hmac-sha512) DQUOTE
headers := "headers" "=" plain-string
signature := "signature" "=" plain-string
plain-string   = DQUOTE *( %x20-21 / %x23-5B / %x5D-7E ) DQUOTE

Signature Parameters

Signature String Construction

In order to generate the string that is signed with a key, the client MUST take the values of each HTTP header specified by headers in the order they appear.

1. If the header name is not request-line then append the lowercased header name followed with an ASCII colon : and an ASCII space ` `.

2. If the header name is request-line then append the HTTP request line (in ASCII format), otherwise append the header value.

3. If value is not the last value then append an ASCII newline \n. The string MUST NOT include a trailing ASCII newline.

Clock Skew

The HMAC Authentication plugin also implements a clock skew check as described in the specification to prevent replay attacks. By default, a minimum lag of 300s in either direction (past/future) is allowed. Any request with a higher or lower date value will be rejected. The length of the clock skew can be edited through the plugin’s configuration by setting the clock_skew property (config.clock_skew POST parameters).

The server and requesting client should be synchronized with NTP and a valid date (using GMT format) should be sent with either the X-Date or Date header.

Body Validation

User can set config.validate_request_body as true to validate the request body. If it’s enabled the plugin will calculate the SHA-256 HMAC digest of the request body and match it against the value of the Digest header. The Digest header needs to be in following format:

Digest: SHA-256=base64(sha256(<body>))

If there is no request body, the Digest should be set to the digest of a body of 0 length.

Note: In order to create the digest of a request body, the plugin needs to retain it in memory, which might cause pressure on the worker’s Lua VM when dealing with large bodies (several MBs) or during high request concurrency.

Enforcing Headers

config.enforce_headers can be used to enforce any of the headers to be part of the signature creation. By default, the plugin doesn’t enforce which header needs to be used for the signature creation. The minimum recommended data to sign is the request-line, host, and date. A strong signature would include all of the headers and a digest of the body.

HMAC Example

The HMAC plugin can be enabled on a Service or a Route.

Create a Service

  $ curl -i -X POST http://localhost:8001/services \
      -d "name=example-service" \
      -d "url=http://example.com"
  HTTP/1.1 201 Created
  ...

Then create a Route

  $ curl -i -f -X POST http://localhost:8001/services/example-service/routes \
      -d "paths[]=/"
  HTTP/1.1 201 Created
  ...

Enabling the plugin on a Service

Plugins can be enabled on a Service or a Route. This example uses a Service.

  $ curl -i -X POST http://localhost:8001/services/example-service/plugins \
      -d "name=hmac-auth" \
      -d "config.enforce_headers=date, request-line" \
      -d "config.algorithms=hmac-sha1, hmac-sha256"
  HTTP/1.1 201 Created
  ...

Add a Consumer

  $ curl -i -X POST http://localhost:8001/consumers/ \
      -d "username=alice"
  HTTP/1.1 201 Created
  ...

Add credential for Alice

  $ curl -i -X POST http://localhost:8001/consumers/alice/hmac-auth \
      -d "username=alice123" \
      -d "secret=secret"
  HTTP/1.1 201 Created
  ...

Making an authorized request

  $ curl -i -X GET http://localhost:8000/requests \
      -H "Host: hmac.com" \
      -H "Date: Thu, 22 Jun 2017 17:15:21 GMT" \
      -H 'Authorization: hmac username="alice123", algorithm="hmac-sha256", headers="date request-line", signature="ujWCGHeec9Xd6UD2zlyxiNMCiXnDOWeVFMu5VeRUxtw="'
  HTTP/1.1 200 OK
  ...

In the above request, we are composing the signing string using the date and request-line headers and creating the digest using the hmac-sha256 to hash the digest:

  signing_string="date: Thu, 22 Jun 2017 17:15:21 GMT\nGET /requests HTTP/1.1"
  digest=HMAC-SHA256(<signing_string>, "secret")
  base64_digest=base64(<digest>)

So the final value of the Authorization header would look like:

  Authorization: hmac username="alice123", algorithm="hmac-sha256", headers="date request-line", signature=<base64_digest>"

Validating request body

To enable body validation we would need to set config.validate_request_body to true:

The following example works the same way, whether the plugin was added to a Service or a Route.

  $ curl -i -X PATCH http://localhost:8001/plugins/{plugin-id} \
      -d "config.validate_request_body=true"
  HTTP/1.1 200 OK
  ...

Now if the client includes the body digest in the request as the value of the Digest header, the plugin will validate the request body by calculating the SHA-256 of the body and matching it against the Digest header’s value.

  $ curl -i -X GET http://localhost:8000/requests \
      -H "Host: hmac.com" \
      -H "Date: Thu, 22 Jun 2017 21:12:36 GMT" \
      -H "Digest: SHA-256=SBH7QEtqnYUpEcIhDbmStNd1MxtHg2+feBfWc1105MA=" \
      -H 'Authorization: hmac username="alice123", algorithm="hmac-sha256", headers="date request-line digest", signature="gaweQbATuaGmLrUr3HE0DzU1keWGCt3H96M28sSHTG8="' \
      -d "A small body"
  HTTP/1.1 200 OK
  ...

In the above request we calculated the SHA-256 digest of the body and set the Digest header with the following format:

  body="A small body"
  digest=SHA-256(body)
  base64_digest=base64(digest)
  Digest: SHA-256=<base64_digest>

Upstream Headers

When a client has been authenticated, the plugin will append some headers to the request before proxying it to the upstream service, so that you can identify the Consumer in your code:

• X-Consumer-ID, the ID of the Consumer on Kong
• X-Consumer-Custom-ID, the custom_id of the Consumer (if set)
• X-Consumer-Username, the username of the Consumer (if set)
• X-Credential-Username, the username of the Credential (only if the consumer is not the ‘anonymous’ consumer)
• X-Anonymous-Consumer, will be set to true when authentication failed, and the ‘anonymous’ consumer was set instead.

You can use this information on your side to implement additional logic. You can use the X-Consumer-ID value to query the Kong Admin API and retrieve more information about the Consumer.

Paginate through the HMAC Credentials

You can paginate through the hmac-auth Credentials for all Consumers using the following request:

$ curl -X GET http://kong:8001/hmac-auths

{
    "total": 3,
    "data": [
        {
            "created_at": 1509681246000,
            "id": "75695322-e8a0-4109-aed4-5416b0308d85",
            "secret": "wQazJ304DW5huJklHgUfjfiSyCyTAEDZ",
            "username": "foo",
            "consumer": { "id": "c0d92ba9-8306-482a-b60d-0cfdd2f0e880" }
        },
        {
            "created_at": 1509419793000,
            "id": "11d5cbfb-31b9-4a6d-8496-2f4a76500643",
            "secret": "zi6YHyvLaUCe21XMXKesTYiHSWy6m6CW",
            "username": "bar",
            "consumer": { "id": "3c2c8fc1-7245-4fbb-b48b-e5947e1ce941" }
        },
        {
            "created_at": 1509681215000,
            "id": "eb0365bc-88ae-4568-be7c-db1eb7c16e5e",
            "secret": "NvHDTg5mp0ySFVJsITurtgyhEq1Cxbnv",
            "username": "baz",
            "consumer": { "id": "c0d92ba9-8306-482a-b60d-0cfdd2f0e880" }
        }
    ]
}

You can filter the list by consumer by using this other path:

$ curl -X GET http://kong:8001/consumers/{username or id}/hmac-auth

{
    "total": 1,
    "data": [
        {
            "created_at": 1509419793000,
            "id": "11d5cbfb-31b9-4a6d-8496-2f4a76500643",
            "secret": "zi6YHyvLaUCe21XMXKesTYiHSWy6m6CW",
            "username": "bar",
            "consumer": { "id": "3c2c8fc1-7245-4fbb-b48b-e5947e1ce941" }
        }
    ]
}

username or id: The username or id of the consumer whose credentials need to be listed

Retrieve the Consumer associated with a Credential

It is possible to retrieve a Consumer associated with an HMAC Credential using the following request:

curl -X GET http://kong:8001/hmac-auths/{hmac username or id}/consumer

{
   "created_at":1507936639000,
   "username":"foo",
   "id":"c0d92ba9-8306-482a-b60d-0cfdd2f0e880"
}

hmac username or id: The id or username property of the HMAC Credential for which to get the associated Consumer. Note that username accepted here is not the username property of a Consumer.