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, Emissary load-balances between them 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/v3alpha1. Earlier versions are deprecated.

Example

---
apiVersion: getambassador.io/v3alpha1
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 (none; a value is required) Identifies the external auth service to talk to. The format of this field is scheme://host:port where scheme:// and :port are optional. The scheme-part, if present, must be either http:// or https://; if the scheme-part is not present, it behaves as if http:// is given. The scheme-part controls whether TLS or plaintext is used and influences the default value of the port-part. The host-part must be the namespace-qualified DNS name of the service you want to use for authentication.
tls "" This field is populated with the name of the defined TLSContext, which determines the TLS certificate presented to external auth services.
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.
include_body.max_bytes (none; a value is required if include_body is not null) Controls the amount of body data that is passed to the external auth service.
include_body.allow_partial (none; a value is required if include_body is not null) 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 Controls whether to allow or reject requests when there is an error communicating with the external auth service; a value of true allows the request through to the upstream backend service, a value of false returns a status_on_error.code response to the client.
stats_name the auth_service value with non-alphanumeric characters replaced with underscores See Overriding Statistics Names.
circuit_breakers the value set in the ambassador Module See Circuit Breakers.

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 Controls the gRPC service name used to communicate with the AuthService. Allowed values are v2, which uses the envoy.service.auth.v2.Authorization service name; and v3, which uses the envoy.service.auth.v3.Authorization service name. v3 cannot be used with the AMBASSADOR_ENVOY_API_VERSION=V2 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 (case-insensitive) that are copied from the incoming request to the request made to the external auth service. 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 (case-insensitive) that are 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 are 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.

Transport Protocol Migration

Note: The following information is only applicable to AuthServices using proto: grpc As of Emissary version 2.3, the v2 transport protocol is deprecated and any AuthServices making use of it should migrate to v3 before support for v2 is removed in a future release.

The following imports simply need to be updated to migrate an AuthService

v2 Imports:

	envoyCoreV2 "github.com/datawire/ambassador/pkg/api/envoy/api/v2/core"
	envoyAuthV2 "github.com/datawire/ambassador/pkg/api/envoy/service/auth/v2"
	envoyType "github.com/datawire/ambassador/pkg/api/envoy/type"

v3 Imports:

	envoyCoreV3 "github.com/datawire/ambassador/v2/pkg/api/envoy/config/core/v3"
	envoyAuthV3 "github.com/datawire/ambassador/v2/pkg/api/envoy/service/auth/v3"
	envoyType "github.com/datawire/ambassador/v2/pkg/api/envoy/type/v3"

Last modified August 8, 2024: Update all 2.5 resources with appropriate metadata (aa2bcaf)