Error when using @EnableWebFluxSecurity in springboot

Question

Currently I´m trying to integrate JWT Authentication in an existing Spring Boot Webflux Project. As a template I used this medium article: https://medium.com/@ard333/authentication-and-authorization-using-jwt-on-spring-webflux-29b81f813e78.
If I put the Annotation @EnableWebFluxSecurity inside my WebSecurityConfig the following error occurs:

The bean 'conversionServicePostProcessor', defined in class path resource [org/springframework/security/config/annotation/web/configuration/WebSecurityConfiguration.class], could not be registered. A bean with that name has already been defined in class path resource [org/springframework/security/config/annotation/web/reactive/WebFluxSecurityConfiguration.class] and overriding is disabled.

Basicaly it´s the same error as in this post Error creating bean named `conversionServicePostProcessor` when using spring-boot-admin-server but the answers didn´t help for me and I can´t comment on answers.

In the previous post two solutions are mentioned that didn´t work for me. Removing the websocket dependency didn´t help and setting "spring.main.allow-bean-definition-overriding=true" seems to override my own Configuration, because my route /auth/login/guest is still responding 401.

Here is my WebSecurityConfiguration:

package de.thm.arsnova.frag.jetzt.backend.config;

import de.thm.arsnova.frag.jetzt.backend.security.AuthenticationManager;
import de.thm.arsnova.frag.jetzt.backend.security.SecurityContextRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.security.config.annotation.method.configuration.EnableReactiveMethodSecurity;
import org.springframework.security.config.annotation.web.reactive.EnableWebFluxSecurity;
import org.springframework.security.config.web.server.ServerHttpSecurity;
import org.springframework.security.web.server.SecurityWebFilterChain;
import reactor.core.publisher.Mono;

@Configuration
@EnableWebFluxSecurity
@EnableReactiveMethodSecurity
public class WebSecurityConfig {

    private final AuthenticationManager authenticationManager;
    private final SecurityContextRepository securityContextRepository;

    @Autowired
    public WebSecurityConfig(AuthenticationManager authenticationManager, SecurityContextRepository securityContextRepository) {
        this.authenticationManager = authenticationManager;
        this.securityContextRepository = securityContextRepository;
    }

    @Bean
    public SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http) {
        return http
                .exceptionHandling()
                .authenticationEntryPoint((swe, e) ->
                        Mono.fromRunnable(() -> swe.getResponse().setStatusCode(HttpStatus.UNAUTHORIZED))
                ).accessDeniedHandler((swe, e) ->
                        Mono.fromRunnable(() -> swe.getResponse().setStatusCode(HttpStatus.FORBIDDEN))
                ).and()
                .csrf().disable()
                .formLogin().disable()
                .httpBasic().disable()
                .authenticationManager(authenticationManager)
                .securityContextRepository(securityContextRepository)
                .authorizeExchange()
                .pathMatchers(HttpMethod.OPTIONS).permitAll()
                .pathMatchers("/auth/login/guest").permitAll()
                .anyExchange().authenticated()
                .and().build();
    }
}

and my pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>de.thm.arsnova.frag.jetzt</groupId>
    <artifactId>frag.jetzt-backend</artifactId>
    <version>0.1.0</version>

    <properties>
        <spring-boot-version>2.3.0.RELEASE</spring-boot-version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>${spring-boot-version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-amqp</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-r2dbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>io.r2dbc</groupId>
            <artifactId>r2dbc-postgresql</artifactId>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.flywaydb</groupId>
            <artifactId>flyway-core</artifactId>
            <version>6.0.8</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt-api</artifactId>
            <version>0.11.1</version>
        </dependency>
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt-impl</artifactId>
            <version>0.11.1</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt-jackson</artifactId>
            <version>0.11.1</version>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
        </dependency>
        <!-- LogBack dependencies -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>jcl-over-slf4j</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.jacoco</groupId>
                <artifactId>jacoco-maven-plugin</artifactId>
                <version>0.8.5</version>
                <executions>
                    <execution>
                        <id>default-prepare-agent</id>
                        <goals>
                            <goal>prepare-agent</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>default-report</id>
                        <phase>prepare-package</phase>
                        <goals>
                            <goal>report</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
                <version>${spring-boot-version}</version>
            </plugin>
            <plugin>
                <groupId>org.flywaydb</groupId>
                <artifactId>flyway-maven-plugin</artifactId>
                <version>6.4.2</version>
                <configuration>
                    <url>jdbc:postgresql://localhost:5432/fragjetzt</url>
                    <user>fragjetzt</user>
                    <password>fragjetzt</password>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

Answer 1

You can add this in test properties/app properties:

spring.main.web-application-type=reactive

This begins to be required when servlet and webflux are both in classpath. Check here: https://docs.spring.io/spring-boot/docs/2.3.1.RELEASE/reference/html/spring-boot-features.html#boot-features-testing-spring-boot-applications-detecting-web-app-type