Authentication service

Emissary provides a highly flexible mechanism for authentication, via the AuthService resource. An AuthService configures Emissary to use an external service to check authentication and authorization for incoming requests. Each incoming request is authenticated before routing to its destination.

All requests are validated by the AuthService (unless the Mapping applied to the request sets bypass_auth). It is not possible to combine multiple AuthServices. While it is possible to create multiple AuthService resources, they will be load-balanced between each resource in a round-robin fashion. This is useful for canarying an AuthService change, but is not useful for deploying multiple distinct AuthServices. In order to combine multiple external services (either having multiple services apply to the same request, or selecting between different services for the different requests), instead of using an AuthService, use an Ambassador Edge Stack External Filter.

Because of the limitations described above, Ambassador Edge Stack does not support AuthService resources, and you should instead use an External Filter, which is mostly a drop-in replacement for an AuthService. The External Filter relies on the Ambassador Edge Stack AuthService. Make sure the Ambassador Edge Stack AuthService is deployed before configuring External filters.

The currently supported version of the AuthService resource is getambassador.io/v2. Earlier versions are deprecated.

Example

---
apiVersion: getambassador.io/v2
kind: AuthService
metadata:
  name: authentication
spec:
  ambassador_id: ambassador-1
  auth_service: "example-auth.authentication:3000"
  tls: true
  proto: http
  timeout_ms: 5000
  include_body:
    max_bytes: 4096
    allow_partial: true
  status_on_error:
    code: 403
  failure_mode_allow: false

  # proto: grpc only
  protocol_version: v2

  # proto: http only
  path_prefix: "/path"
  allowed_request_headers:
  - "x-example-header"
  allowed_authorization_headers:
  - "x-qotm-session"
  add_auth_headers:
    x-added-auth: auth-added
  add_linkerd_headers: false

Fields

auth-service is the only required field, all others are optional.

Attribute Default value Description
ambassador_id default Which Ambassador ID the AuthService should apply to.
auth_service n/a Formatted like [scheme://]host[:port], identifies the external auth service to talk to. The scheme-part may be http:// or https://, which influences the default value of tls, and of the port-part. If no scheme-part is given, it behaves as if http:// was given. The host should be the namespace-qualified DNS name of the service you want to use for authentication.
tls true if auth_service starts with “https://” Whether to use TLS or cleartext when speaking to the external auth service. The default is based on the scheme-part of the auth_service. If the value of tls is not a Boolean, the value is taken to be the name of a defined TLSContext, which will determine the certificate presented to the upstream service.
proto http Specifies which variant of the ext_authz protocol to use when communicating with the external auth service. Valid options are http or grpc.
timeout_ms 5000 The total maximum duration in milliseconds for the request to the external auth service, before triggering status_on_error or failure_mode_allow.
include_body null Controls how much to buffer the request body to pass to the external auth service, for use cases such as computing an HMAC or request signature. If include_body is null or unset, then the request body is not buffered at all, and an empty body is passed to the external auth service. If include_body is not null, the max_bytes and allow_partial subfields are required. max_bytes controls the amount of body data that will be passed to the external auth service. allow_partial controls what happens to requests with bodies larger than max_bytes. If allow_partial is true, the first max_bytes of the body are sent to the external auth service. If false, the message is rejected with HTTP 413 (“Payload Too Large”).
status_on_error.code 403 Controls the status code returned when unable to communicate with external auth service. This is ignored if failure_mode_allow: true.
failure_mode_allow false Setting to true will allow the request through to the upstream backend service if there is an error communicating with the external auth service, instead of returning status_on_error.code to the client.

The following field is only used if proto is set to grpc. It is ignored if proto is http.

Attribute Default value Description
protocol_version v2 gRPC service name used to communicate with the AuthService. Allowed values are v2 which will use the envoy.service.auth.v2.Authorization service name, and v3 which will use the envoy.service.auth.v3.Authorization service name. v3 requires Emissary to run in Envoy v3 mode by setting the AMBASSADOR_ENVOY_API_VERSION=V3 environment variable.

The following fields are only used if proto is set to http. They are ignored if proto is grpc.

Attribute Default value Description
path_prefix "" Prepends a string to the request path of the request when sending it to the external auth service. By default this is empty, and nothing is prepended. For example, if the client makes a request to /foo, and path_prefix: /bar, then the path in the request made to the external auth service will be /foo/bar.
allowed_request_headers [] lists the headers that will be sent copied from the incoming request to the request made to the external auth service (case-insensitive). In addition to the headers listed in this field, the following headers are always included: Authorization, Cookie, From, Proxy-Authorization, User-Agent, X-Forwarded-For, X-Forwarded-Host, and X-Forwarded-Proto.
allowed_authorization_headers [] Lists the headers that will be copied from the response from the external auth service to the request sent to the upstream backend service (if the external auth service indicates that the request to the upstream backend service should be allowed). In addition to the headers listed in this field, the following headers are always included: Authorization, Location, Proxy-Authenticate, Set-cookie, WWW-Authenticate
add_auth_headers {} A dictionary of header: value pairs that will be added to the request made to the external auth service.
add_linkerd_headers Defaults to the value set in the ambassador Module When true, in the request to the external auth service, adds an l5d-dst-override HTTP header that is set to the hostname and port number of the external auth service.

Canarying multiple AuthServices

You may create multiple AuthService manifests to round-robin authentication requests among multiple services. All services must use the same path_prefix and header definitions. If you try to have different values, you’ll see an error in the diagnostics service, telling you which value is being used.

Configuring public Mappings

An AuthService can be disabled for a Mapping by setting bypass_auth to true. This will tell Emissary to allow all requests for that Mapping through without interacting with the external auth service.


Last modified September 9, 2024: Update all 1.14 metadata to fix navigation (c0afada)