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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 the Play filters project to your libraryDependencies in build.sbt:

libraryDependencies += filters

Now add the CORS filter to your filters, which is typically done by creating a Filters class in the root of your project:

Scala

import javax.inject.Inject

import play.api.http.HttpFilters
import play.filters.cors.CORSFilter

class Filters @Inject() (corsFilter: CORSFilter) extends HttpFilters {
  def filters = Seq(corsFilter)
}

Java

import play.mvc.EssentialFilter;
import play.filters.cors.CORSFilter;
import play.http.HttpFilters;

import javax.inject.Inject;

public class Filters implements HttpFilters {

    @Inject
    CORSFilter corsFilter;

    public EssentialFilter[] filters() {
        return new EssentialFilter[] { corsFilter.asJava() };
    }
}

The Filters class can either be in the root package, or if it has another name or is in another package, needs to be configured using play.http.filters in application.conf:

play.http.filters = "filters.MyFilters"

§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 with origins from a whitelist (by default all origins are allowed)
• 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)

For example:

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

Next: Configuring allowed hosts