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CORS

A CORS (Cross-origin resource sharing) policy can be set for a HTTPProxy in order to allow cross-domain requests for trusted sources. If a policy is set, it will be applied to all the routes of the virtual host.

Contour allows configuring the headers involved in responses to cross-domain requests. These include the Access-Control-Allow-Origin, Access-Control-Allow-Methods, Access-Control-Allow-Headers, Access-Control-Expose-Headers, Access-Control-Max-Age, and Access-Control-Allow-Credentials headers in responses.

In this example, cross-domain requests will be allowed for any domain (note the * value), with the methods GET, POST, or OPTIONS. Headers Authorization and Cache-Control will be passed to the upstream server and headers Content-Length and Content-Range will be made available to the cross-origin request client.

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: cors-example
spec:
  virtualhost:
    fqdn: www.example.com
    corsPolicy:
        allowCredentials: true
        allowOrigin:
          - "*" # allows any origin
        allowMethods:
          - GET
          - POST
          - OPTIONS
        allowHeaders:
          - authorization
          - cache-control
        exposeHeaders:
          - Content-Length
          - Content-Range
        maxAge: "10m" # preflight requests can be cached for 10 minutes.
  routes:
    - conditions:
      - prefix: /
      services:
        - name: cors-example
          port: 80

The allowOrigin list may also be configured with exact origin matches or regex patterns. In the following example, cross-domain requests must originate from the domain https://client.example.com or domains that match the regex http[s]?:\/\/some-site-[a-z0-9]+\.example\.com (e.g. request with Origin header https://some-site-abc456.example.com)

Note: Patterns for matching Origin headers must be valid regex, simple “globbing” patterns (e.g. *.foo.com) will not be accepted or may produce incorrect matches.

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: cors-example
spec:
  virtualhost:
    fqdn: www.example.com
    corsPolicy:
        allowCredentials: true
        allowOrigin:
          - https://client.example.com
          - http[s]?:\/\/some-site-[a-z0-9]+\.example\.com
        allowMethods:
          - GET
          - POST
          - OPTIONS
        allowHeaders:
          - authorization
          - cache-control
        exposeHeaders:
          - Content-Length
          - Content-Range
        maxAge: "10m"
  routes:
    - conditions:
      - prefix: /
      services:
        - name: cors-example
          port: 80

MaxAge durations are expressed in the Go duration format. Valid time units are “ns”, “us” (or “┬Ás”), “ms”, “s”, “m”, “h”. Only positive values are allowed and 0 disables the cache requiring a preflight OPTIONS check for all cross-origin requests.

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