Filters and Authentication

Filters are used to extend the Ambassador Edge Stack to modify or intercept a request before sending to your backend service. The most common use case for Filters is authentication, and Edge Stack includes a number of built-in filters for this purpose. Edge Stack also supports developing custom filters.

Filters are managed using a FilterPolicy resource. The FilterPolicy resource specifies a particular host or URL to match, along with a set of filters to run when an request matches the host/URL.

Filter Types

Edge Stack supports the following filter types:

• JWT, which validates JSON Web Tokens
• OAuth2, which performs OAuth2 authorization against an identity provider implementing OIDC Discovery.
• Plugin, which allows users to write custom Filters in Go that run as part of the Edge Stack container
• External, which allows users to call out to other services for request processing. This can include both custom services (in any language) or third party services.

Managing Filters

Filters are created with the Filter resource type, which contains global arguments to that filter. Which Filter(s) to use for which HTTP requests is then configured in FilterPolicy resources, which may contain path-specific arguments to the filter.

Filter Definition

Filters are created as Filter resources. The body of the resource spec depends on the filter type:

---
apiVersion: getambassador.io/v2
kind: Filter
metadata:
  name:      "string"      # required; this is how to refer to the Filter in a FilterPolicy
  namespace: "string"      # optional; default is the usual `kubectl apply` default namespace
spec:
  ambassador_id:           # optional; default is ["default"]
  - "string"
  ambassador_id: "string"  # no need for a list if there's only one value
  FILTER_TYPE:
    GLOBAL_FILTER_ARGUMENTS

FilterPolicy Definition

FilterPolicy resources specify which filters (if any) to apply to which HTTP requests.

---
apiVersion: getambassador.io/v2
kind: FilterPolicy
metadata:
  name: "example-filter-policy"
  namespace: "example-namespace"
spec:
  rules:
  - host: "glob-string"
    path: "glob-string"
    filters:                    # optional; omit or set to `null` or `[]` to apply no filters to this request
    - name: "string"              # required
      namespace: "string"         # optional; default is the same namespace as the FilterPolicy
      ifRequestHeader:            # optional; default to apply this filter to all requests matching the host & path
        name: "string"              # required
        negate: bool                # optional; default is false
        # It is invalid to specify both "value" and "valueRegex".
        value: "string"             # optional; default is any non-empty string
        valueRegex: "regex-string"  # optional; default is any non-empty string
      onDeny: "enum-string"       # optional; default is "break"
      onAllow: "enum-string"      # optional; default is "continue"
      arguments: DEPENDS          # optional

Rule configuration values include:

The wildcard * is supported for both path and host.

The type of the arguments property is dependent on which Filter type is being referred to; see the "Path-Specific Arguments" documentation for each Filter type.

When multiple Filters are specified in a rule:

• The filters are gone through in order
• Each filter may either
  1. return a direct HTTP response, intended to be sent back to the requesting HTTP client (normally denying the request from being forwarded to the upstream service); or
  2. return a modification to make to the HTTP request before sending it to other filters or the upstream service (normally allowing the request to be forwarded to the upstream service with modifications).
• If a filter has an ifRequestHeader setting, the filter is skipped unless the request (including any modifications made by earlier filters) has the HTTP header field name (case-insensitive) either set to (if negate: false) or not set to (if negate: true)
  • a non-emtpy string if neither value nor valueRegex are set
  • the exact string value (case-sensitive) (if value is set)
  • a string that matches the regular expression valueRegex (if valueRegex is set). This uses [RE2][] syntax (always, not obeying [regex_type][] in the Ambassador module) but does not support the \C escape sequence.
• onDeny identifies what to do when the filter returns an "HTTP response":
  • "break": End processing, and return the response directly to the requesting HTTP client. Later filters are not called. The request is not forwarded to the upstream service.
  • "continue": Continue processing. The request is passed to the next filter listed; or if at the end of the list, it is forwarded
  • "continue": Continue processing. The request is passed to the next filter listed; or if at the end of the list, it is forwarded to the upstream service. The HTTP response returned from the filter is discarded.
• onAllow identifies what to do when the filter returns a "modification to the HTTP request":
  • "break": Apply the modification to the request, then end filter processing, and forward the modified request to the upstream service. Later filters are not called.
  • "continue": Continue processing. Apply the request modification, then pass the modified request to the next filter listed; or if at the end of the list, forward it to the upstream service.
• Modifications to the request are cumulative; later filters have access to all headers inserted by earlier filters.

FilterPolicy Example

In the example below, the param-filter Filter Plugin is loaded, and configured to run on requests to /httpbin/.

---
apiVersion: getambassador.io/v2
kind: Filter
metadata:
  name: param-filter # This is the name used in FilterPolicy
  namespace: standalone
spec:
  Plugin:
    name: param-filter # The plugin's `.so` file's base name
---
apiVersion: getambassador.io/v2
kind: FilterPolicy
metadata:
  name: httpbin-policy
spec:
  rules:
  # Don't apply any filters to requests for /httpbin/ip
  - host: "*"
    path: /httpbin/ip
    filters: null
  # Apply param-filter and auth0 to requests for /httpbin/
  - host: "*"
    path: /httpbin/*
    filters:
    - name: param-filter
    - name: auth0
  # Default to authorizing all requests with auth0
  - host: "*"
    path: "*"
    filters:
    - name: auth0

Note: The Ambassador Edge Stack will choose the first FilterPolicy rule that matches the incoming request. As in the above example, you must list your rules in the order of least to most generic.

Multiple Domains

In this example, the foo-keycloak filter is used for requests to foo.bar.com, while the example-auth0 filter is used for requests to example.com. This configuration is useful if you are hosting multiple domains in the same cluster.

apiVersion: getambassador.io/v2
kind: FilterPolicy
metadata:
  name: multi-domain-policy
spec:
  rules:
  - host: foo.bar.com
    path: "*"
    filters:
      - name: foo-keycloak
  - host: example.com
    path: "*"
    filters:
      - name: example-auth0

Installing self-signed certificates

The JWT and OAuth2 filters speak to other services over HTTP or HTTPS. If those services are configured to speak HTTPS using a self-signed certificate, attempting to talk to them will result in an error mentioning ERR x509: certificate signed by unknown authority. You can fix this by installing that self-signed certificate into the AES container following the standard procedure for Alpine Linux 3.8: Copy the certificate to /usr/local/share/ca-certificates/ and then run update-ca-certificates. Note that the aes image sets USER 1000, but that update-ca-certificates needs to be run as root.

FROM docker.io/datawire/aes:1.12.0
USER root
COPY ./my-certificate.pem /usr/local/share/ca-certificates/my-certificate.crt
RUN update-ca-certificates
USER 1000

When deploying the Ambassador Edge Stack, refer to that custom Docker image, rather than to docker.io/datawire/aes:1.12.0