AuthService Plugin

The Ambassador API Gateway provides a highly flexible mechanism for authentication, via the AuthService resource. An AuthService configures Ambassador 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 Ambassador Edge Stack External Filter.

Because of the limitations described above, the 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.

Configure an External AuthService

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

---
apiVersion: getambassador.io/v2
kind: AuthService
metadata:
  name: authentication
spec:
  ambassador_id: string-or-string-list # optional; default is ["default"]
  auth_service: "example-auth:3000" # required
  tls: true                         # optional; default is true if `auth_service` starts with "https://" (case-insensitive), false otherwise
  proto: http                       # optional; default is "http"
  timeout_ms: 5000                  # optional; default is 5000
  #allow_request_body: true         # deprecated; use include_body instead
  include_body:                     # optional; default is null
    max_bytes: 4096                   # required
    allow_partial: true               # required
  status_on_error:                  # optional
    code: 503                         # optional; default is 403
  failure_mode_allow: false         # optional; default is false
  # the following are used only if `proto: http`; they are ignored if `proto: grpc`
  path_prefix: "/path"             # optional; default is ""
  allowed_request_headers:         # optional; default is []
  - "x-example-header"
  allowed_authorization_headers:   # optional; default is []
  - "x-qotm-session"
  add_auth_headers:                # optional; default is {}
    x-added-auth: auth-added
  add_linkerd_headers: bool        # optional; default is based on the ambassador Module

• auth_service (required) is of the format [scheme://]host[:port], and 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.

• tls (optional) is 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 (optional) specifies which variant of the [ext_authz protocol][] to use when communicating with the external auth service. Valid options are http (default) or grpc.

• timeout_ms (optional) is the total maximum duration in milliseconds for the request to the external auth service, before triggering status_on_error or failure_mode_allow.

• allow_request_body (optional, deprecated) controls whether to buffer the request body in order to pass to the external auth service. Setting allow_request_body: true is exactly equivalent to include_body: { max_bytes: 4096, allow_partial: true }, and allow_request_body: false is exactly equivalent to include_body: null. It is invalid to set both allow_request_body and include_body.

• include_body (optional) 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, both of its sub-fields are required:

  • max_bytes (required) controls the amount of body data that will be passed to the external auth service
  • allow_partial (required) 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 (optional) controls the status code returned when unable to communicate with external auth service. This is ignored if failure_mode_allow: true.

  • code (optional) defaults to 403.

• failure_mode_allow (optional) being set to true causes the request to be allowed 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 Defaults to false.

The following fields are only used if proto: http; they are ignored if proto: grpc:

• path_prefix (optional) 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 (optional) 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
  • X-Forwarded-Proto

• allowed_authorization_headers (optional) 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 (optional) is a dictionary of header: value pairs that will be added to the request made to the external auth service.

• add_linkerd_headers (optional) 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. Defaults to the value set in the ambassador Module.

Detailed ext_authz protocol documentation.

Canarying Multiple AuthServices

You may create multiple AuthService manifests to round-robin authentication requests among multiple services. Note well that 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 Ambassador to allow all requests for that mapping through without interacting with the external auth service.