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4. Built-in HTTP filters

§Cross-Origin Resource Sharing

Play provides a filter that implements Cross-Origin Resource Sharing (CORS).

CORS is a protocol that allows web applications to make requests from the browser across different domains. A full specification can be found here.

§Enabling the CORS filter

To enable the CORS filter, add play.filters.cors.CORSFilter to application.conf:

play.filters.enabled += "play.filters.cors.CORSFilter"

§Configuring the CORS filter

The filter can be configured from application.conf. For a full listing of configuration options, see the Play filters reference.conf.

The available options include:

• play.filters.cors.pathPrefixes - filter paths by a whitelist of path prefixes
• play.filters.cors.allowedOrigins - allow only requests from origins in this whitelist. By default the value is null, which means allow all origins. The value "*" has a special meaning, it will send back Access-Control-Allow-Origin: * if the request origin does not match any other origins in the list. "null" is treated as a valid origin, and can be whitelisted in allowedOrigins to allow origins with non-hierarchical schemes like file: and data: by sending Access-Control-Allow-Origin: "null". Be aware that this is discouraged by the W3C as it can also grant hostile documents access to the response.
• play.filters.cors.allowedHttpMethods - allow only HTTP methods from a whitelist for preflight requests (by default all methods are allowed)
• play.filters.cors.allowedHttpHeaders - allow only HTTP headers from a whitelist for preflight requests (by default all headers are allowed)
• play.filters.cors.exposedHeaders - set custom HTTP headers to be exposed in the response (by default no headers are exposed)
• play.filters.cors.supportsCredentials - disable/enable support for credentials (by default credentials support is enabled)
• play.filters.cors.preflightMaxAge - set how long the results of a preflight request can be cached in a preflight result cache (by default 1 hour)
• play.filters.cors.serveForbiddenOrigins - enable/disable serving requests with origins not in whitelist as non-CORS requests (by default they are forbidden)

For example:

play.filters.cors {
  pathPrefixes = ["/some/path", ...]
  allowedOrigins = ["http://www.example.com", ...]
  allowedHttpMethods = ["GET", "POST"]
  allowedHttpHeaders = ["Accept"]
  preflightMaxAge = 3 days
}

Next: Configuring CSP

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