Springfox Swagger UI behind reverse proxy

Question

I have configured a Spring Boot application with Swagger API documentation and configured Swagger UI.

I also run my backend application behind a reverse proxy that maps all requests from host:port/api to backend_host:port/, when running locally on localhost I map localhost:8082/api. In production a similar mapping is applied.

When I open the Swagger UI from localhost:8082/api/swagger-ui.html it shows the following lines below the title:

[ Base URL: localhost:8080 ]
http://localhost:8082/api/v2/api-docs

When I invoke any rest operation swagger always tries to perform it against localhost:8080 which then fails due to the same origin policy.

I am aware of using pathProvider but it only affects the base URL's path part, not the domain and port. So I can only use it to change the base URL to localhost:8080/api but I would need it to change to localhost:8082/api. Is there a way to set the host dynamically to the current host and port that is active in the browser?

.pathProvider (new RelativePathProvider (servletContext) {
                @Override
                public String getApplicationBasePath() {
                    return "/api";
                }
               })

Answer 1

In my case with a spring-boot:2.2.6 application with springdoc-openapi-ui:1.3.0 (that also has embedded the swagger UI), I solved the proxy problem setting the server URL in this way:

@Configuration
public class OpenApiConfig {

  @Value("${server}")
  private String url;

  @Bean
  @Profile("prod")
  public OpenAPI customConfiguration() {
    return new OpenAPI()
        .servers(Collections
            .singletonList(new Server().url(url))) //real public URL
        .components(new Components())
        .info(new Info().title("Dummy API Docs")
            .description("Dummy REST API documentation"));
  }
}

This change is reflected in the contract (https://real-domain.com/api-docs):

And in the Swagger UI (https://real-domain.com/swagger-ui/index.html?configUrl=/api-docs/swagger-config)

Answer 2

I think in your case you need to configure your proxy to set HTTP Header
(which will be forwarded to your target backend)
to "notify" Swagger endpoints to return custom URL in /apidocs endpoint.

Please configure proxy to set header X-Forwarded-Host to value from Host request header

Explanation:
In your browser when you will visit a url eg. https://my.domain.com/api/swagger-ui.html

the proxy should create and forward header X-Forwarded-Host: my.endpoint.com

to your backend localhost:8082/api/swagger-ui.html

-> so the Swagger /apidocs enpoint could take this header into consideration in response JSON.

My own case - in Microsoft IIS:

I needed to configure Microsoft IIS to serve Swagger IU from Apache Tomcat on 8080 port on HTTPS domain,
so I needed to have following configuration:

<serverVariables>
    <set name="HTTP_X_FORWARDED_HOST" value=“{HTTP_HOST}” />
    <set name="HTTP_X_FORWARDED_PROTO" value="https" />
</serverVariables>