Spring Cloud Openfeign It's not possible to provide a custom Feign.Client when instantiating programatically

Describe the bug When using the .customize() method of FeignClientBuilder it is not possible to provide a custom (ApacheHttp)Client for request executing. The set client will be overriden after the customizer was apllied.

Sample

We have one Interface with definition of the REST Endpoints. We want to use this Interface to contact multiple instances of this service at different URLs. For all of these connections we need seperate HTTPS Client Certificates and Truststores. This configuration needs to be done at runtime when instantiating the Feign Client.

Example Code of Client instantiation:

Feign.Client client = myCustomClientWithCustomSslContext(clientCert, privateKey, trustStore);
String url = "https://example.org";

MyRestClient myRestClient = new FeignClientBuilder(context)
            .forType(MyRestClient.class, "new-context-id")
            .customize(builder -> builder.client(client))
            .url(url)
            .build();

The FeignClient will be created, but the self created (ApacheHttp)Client with the mutual TLS configuration will be replaced by a default client created when the FeignContext gets initialized.

This happens at FeignClientFactoryBean#getTarget() (https://github.com/spring-cloud/spring-cloud-openfeign/blob/261fc58a5ef0d6f651e66ebca4d958167ebec942/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignClientFactoryBean.java#L409). We set our custom ApacheHttpClient as a customizer. The customizers are applied within this method call: https://github.com/spring-cloud/spring-cloud-openfeign/blob/261fc58a5ef0d6f651e66ebca4d958167ebec942/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignClientFactoryBean.java#L412

At this moment the ApacheHttpClient is set to the builder as expected. But a few lines later it will be overriden with the default one: https://github.com/spring-cloud/spring-cloud-openfeign/blob/261fc58a5ef0d6f651e66ebca4d958167ebec942/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/FeignClientFactoryBean.java#L432-L444

Maybe there is a workaround to archive what a want at another way, but at the moment I don't have any clue. I will provide a PR to adress this issue in a few hours.

Comment From: OlgaMaciaszek

@f11h Thanks for reporting this issue. I was able to reproduce it.