Ktor 1.5.4 Help


Ktor by default provides an interceptor for implementing proper support for Cross-Origin Resource Sharing (CORS).


First of all, install the CORS feature into your application.

fun Application.main() { ... install(CORS) ... }

The default configuration to the CORS feature handles only GET, POST and HEAD HTTP methods and the following headers:

HttpHeaders.Accept HttpHeaders.AcceptLanguages HttpHeaders.ContentLanguage HttpHeaders.ContentType


Here is an advanced example that demonstrates most of CORS-related API functions

fun Application.main() { ... install(CORS) { method(HttpMethod.Options) header(HttpHeaders.XForwardedProto) anyHost() host("my-host") // host("my-host:80") // host("my-host", subDomains = listOf("www")) // host("my-host", schemes = listOf("http", "https")) allowCredentials = true allowNonSimpleContentTypes = true maxAge = Duration.ofDays(1) } ... }


  • method("HTTP_METHOD"): Includes this method to the white list of Http methods to use CORS.

  • header("header-name"): Includes this header to the white list of headers to use CORS.

  • exposeHeader("header-name"): Exposes this header in the response.

  • exposeXHttpMethodOverride(): Exposes X-Http-Method-Override header in the response

  • anyHost(): Allows any host to access the resources

  • host("hostname"): Allows only the specified host to use CORS, it can have the port number, a list of subDomains or the supported schemes.

  • allowCredentials: Includes Access-Control-Allow-Credentials header in the response

  • allowNonSimpleContentTypes: Inclues Content-Type request header to the white list for values other than simple content types.

  • maxAge: Includes Access-Control-Max-Age header in the response with the given max age

Last modified: 11 April 2021