Integrating OAuth2 with Spring Cloud Gateway

Spring Cloud Gateway provides an excellent way to integrate OAuth2 authentication into your microservices architecture. By configuring Spring Cloud Gateway to act as an OAuth2 authentication gateway, you can enforce authentication and authorization rules for incoming requests to your microservices.

To integrate OAuth2 with Spring Cloud Gateway, you need to define a GatewayFilter for OAuth2 validation and route requests accordingly. Here's an example of configuring Spring Cloud Gateway to authorize requests using an OAuth2 authentication server:

1import org.springframework.cloud.gateway.handler.RoutePredicateHandlerMapping;
2import org.springframework.cloud.gateway.route.RouteLocator;
3import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
4import org.springframework.context.annotation.Bean;
5import org.springframework.stereotype.Component;
6
7@Component
8public class GatewayConfig {
9
10    private final String AUTH_SERVER_URL = "http://oauth2-auth-server";
11
12    @Bean
13    public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {
14        return builder.routes()
15            .route("authorize", r -> r
16                .path("/oauth/authorize")
17                .filters(f -> f
18                    .rewritePath("/oauth/authorize", "/oauth2/authorize")
19                    .modifyResponseBody(byte[].class, String.class, (exchange, response) -> {
20                        String modifiedBody = response == null ? "" : response.toUpperCase();
21                        return Mono.just(modifiedBody.getBytes(StandardCharsets.UTF_8));
22                    })
23                    .addRequestHeader("X-Custom-Header", "Custom-Value")
24                    .addRequestParameter("custom-param", "custom-value")
25                )
26                .uri(AUTH_SERVER_URL)
27            )
28            .build();
29    }
30
31}

In this example, we create a custom GatewayConfig class and define a RouteLocator bean for configuring the routes. The RouteLocator is responsible for matching incoming requests and applying filters to modify and route the requests.

The customRouteLocator method creates a route for the /oauth/authorize endpoint using the route method. The filters method is used to define filters for the route, such as:

• rewritePath: Rewrites the path of the request from /oauth/authorize to /oauth2/authorize.
• modifyResponseBody: Modifies the response body to uppercase.
• addRequestHeader: Adds a custom header to the request.
• addRequestParameter: Adds a custom parameter to the request.

Finally, the uri method is used to specify the URL of the OAuth2 authentication server.

By configuring Spring Cloud Gateway with OAuth2 integration, you can easily enforce authentication and authorization rules for your microservices architecture.

Try running the code snippet provided to see how Spring Cloud Gateway routes and modifies requests!

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}

import org.springframework.cloud.gateway.handler.RoutePredicateHandlerMapping;

import org.springframework.cloud.gateway.route.RouteLocator;

import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;

import org.springframework.context.annotation.Bean;

import org.springframework.stereotype.Component;

​

@Component

public class GatewayConfig {

​

    private final String AUTH_SERVER_URL = "http://oauth2-auth-server";

​

    @Bean

    public RouteLocator customRouteLocator(RouteLocatorBuilder builder) {

        return builder.routes()

            .route("authorize", r -> r

                .path("/oauth/authorize")

                .filters(f -> f

                    .rewritePath("/oauth/authorize", "/oauth2/authorize")

                    .modifyResponseBody(byte[].class, String.class, (exchange, response) -> {

                        String modifiedBody = response == null ? "" : response.toUpperCase();

                        return Mono.just(modifiedBody.getBytes(StandardCharsets.UTF_8));

                    })

                    .addRequestHeader("X-Custom-Header", "Custom-Value")

                    .addRequestParameter("custom-param", "custom-value")

                )

                .uri(AUTH_SERVER_URL)

            )

            .build();

    }