TokenRelay

A Token Relay is where an OAuth2 consumer acts as a Client and forwards the incoming token to outgoing resource requests. The consumer can be a pure Client (like an SSO application) or a Resource Server.

Spring Cloud Gateway can forward OAuth2 access tokens downstream to the services it is proxying. To add this functionality to the gateway, you need to add the TokenRelayGatewayFilterFactory like this:

@Bean
public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
    return builder.routes()
            .route("resource", r -> r.path("/resource")
                    .filters(f -> f.tokenRelay())
                    .uri("http://localhost:9000"))
            .build();
}

or this

spring:
  cloud:
    gateway:
      routes:
      - id: resource
        uri: http://localhost:9000
        predicates:
        - Path=/resource
        filters:
        - TokenRelay=

and it will (in addition to logging the user in and grabbing a token) pass the authentication token downstream to the services (in this case /resource).

To enable this for Spring Cloud Gateway add the following dependencies

• org.springframework.boot:spring-boot-starter-oauth2-client

How does it work? The {githubmaster}/src/main/java/org/springframework/cloud/gateway/security/TokenRelayGatewayFilterFactory.java[filter] extracts an access token from the currently authenticated user, and puts it in a request header for the downstream requests.

A TokenRelayGatewayFilterFactory bean will only be created if the proper spring.security.oauth2.client.* properties are set which will trigger creation of a ReactiveClientRegistrationRepository bean.

The default implementation of ReactiveOAuth2AuthorizedClientService used by TokenRelayGatewayFilterFactory uses an in-memory data store. You will need to provide your own implementation ReactiveOAuth2AuthorizedClientService if you need a more robust solution.