Spring Cloud Zuul gateway cannot add custom header to the response - spring-boot

Question

I'm trying to add a custom header to the HTTP response on a Zuul gateway using a post-filter:
#Component
public class ResponseFilter extends ZuulFilter {
private static final Logger logger = LoggerFactory.getLogger(ResponseFilter.class);
#Override
public String filterType() {
return "post";
}
#Override
public int filterOrder() {
return 1;
}
#Override
public boolean shouldFilter() {
return true;
}
#Override
public Object run() {
RequestContext ctx = RequestContext.getCurrentContext();
Object correlationId = ctx.get(FilterUtils.CORRELATION_ID);
if (correlationId != null) {
logger.info("Adding the correlation id to the outbound headers: {}", correlationId);
ctx.getResponse().addHeader(FilterUtils.CORRELATION_ID, correlationId.toString());
// ctx.addZuulResponseHeader(FilterUtils.CORRELATION_ID, correlationId.toString());
}
logger.info("Completing outgoing request for {}", ctx.getRequest().getRequestURI());
return null;
}
}
The application.properties file:
zuul.prefix=/api
ribbon.eureka.enabled=false
spring.cloud.loadbalancer.ribbon.enabled=false
zuul.ignoredHeaders=
zuul.sensitiveHeaders=
The relevant part of pom.xml:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>Greenwich.SR6</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-zuul</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-kubernetes-ribbon</artifactId>
<version>1.1.7.RELEASE</version>
</dependency>
<dependencies>
The gateway is deployed on Openshift 3.11
The problem that I'm having is the fact that the custom header my-correlation-id is ignored by Zuul (does not appear among the response headers).
What am I doing wrong?