CORS

Cross origin resource sharing

Scalatra has CORS support enabled by default. CORS is a security feature from browsers. If a page in a browser wants to do a request to another domain, it will first send an OPTIONS request (called a pre-flight) and depending on the response headers the browser will block or execute the actual request. See the wikipedia page on cross-origin resource sharing for more information.

You can configure your application to be more restrictive by using the following init params.

// List the hosts and ports which will be allowed to make cross-origin requests, 
// separated by commas (* by default).
context.setInitParameter("org.scalatra.cors.allowedOrigins", "http://example.com:8080,http://foo.example.com")

// List what HTTP methods will be accepted. 
// Available options are GET, POST, PUT, DELETE, HEAD, OPTIONS, and PATCH. 
// All methods are accepted by default.
context.setInitParameter("org.scalatra.cors.allowedMethods", "GET")

// Set a list of allowed HTTP headers, most headers are supported.
context.setInitParameter("org.scalatra.cors.allowedHeaders", "Content-Type")

// Set the number of seconds that preflight requests can be cached by the client.
// Default value is 0 seconds.
context.setInitParameter("org.scalatra.cors.preflightMaxAge", "1800")

// By default, cookies are not included in CORS requests. Set this to `true` to allow cookies.
context.setInitParameter("org.scalatra.cors.allowCredentials", "true")

// If CorsSupport needs to be disabled, set to false. Default: CorsSupport is enabled.
context.setInitParameter("org.scalatra.cors.enable", "false")

If you are configuring your application using web.xml, the corresponding xml configuration would be.

<web-app>
   <context-param>
    <param-name>org.scalatra.cors.allowedOrigins</param-name>
    <param-value>*</param-value>
  </context-param>
  <context-param>
    <param-name>org.scalatra.cors.allowCredentials</param-name>
    <param-value>false</param-value>
  </context-param>
   <context-param>
    <param-name>{cors-param-name}</param-name>
    <param-value>{cors-param-value}</param-value>
  </context-param>
  ...
</web-app>

Where {cors-param-name} and {cors-param-value} above represents the supported cors parameters and values respectively.

Special care when allowedOrigins = “*” (which is the default!)

If your init param org.scalatra.cors.allowedOrigins is equal to “*“, which is the default, then you must set org.scalatra.cors.allowCredentials to false. Otherwise the browser will block the request because it could leak credentials to any domain.

Recommended configuration:

// Optional because * is the default
context.setInitParameter("org.scalatra.cors.allowedOrigins", "*")
// Disables cookies, but required because browsers will not allow passing credentials to wildcard domains  
context.setInitParameter("org.scalatra.cors.allowCredentials", "false")

If you need allowedCredentials to be true, then you have to implement an options route and set the allowed domain:

import org.scalatra.CorsSupport

class YourServlet extends ScalatraBase with CorsSupport {

  options("/*"){
    response.setHeader("Access-Control-Allow-Origin", request.getHeader("Origin"))
  }

}

If you’re not familiar with CORS, you may want to find out a bit more about preflightMaxAge and allowCredentials or read the whole spec at the W3C. A good tutorial is also available at HTML5Rocks.