I am developing a web application using Spring Boot 3 with the Undertow web server. I want to integrate Keycloak as the authentication server for the application, which uses the returned token for authorization. After doing that, I encounter an error. However, everything works fine when I switch to using the Tomcat web server. Note that I am using Spring Boot 3.3.5 and Java 21.

Do I have any mistakes while configuring projects?

The error mentioned below:

.springframework.context.ApplicationContextException: Unable to start web server
        at .springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:165) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:619) ~[spring-context-6.1.14.jar:6.1.14]
        at .springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:146) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.SpringApplication.refreshContext(SpringApplication.java:456) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.SpringApplication.run(SpringApplication.java:335) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.SpringApplication.run(SpringApplication.java:1363) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.SpringApplication.run(SpringApplication.java:1352) ~[spring-boot-3.3.5.jar:3.3.5]
        at com.megaheart.mymoney.MymoneyApplication.main(MymoneyApplication.java:17) ~[classes/:na]
Caused by: java.lang.AbstractMethodError: Receiver class .keycloak.adapters.undertow.KeycloakServletExtension does not define or inherit an implementation of the resolved method 'abstract void handleDeployment(io.undertow.servlet.api.DeploymentInfo, jakarta.servlet.ServletContext)' of interface io.undertow.servlet.ServletExtension.
        at io.undertow.servlet.core.DeploymentManagerImpl.handleExtensions(DeploymentManagerImpl.java:282) ~[undertow-servlet-2.3.18.Final.jar:2.3.18.Final]
        at io.undertow.servlet.core.DeploymentManagerImpl.deploy(DeploymentManagerImpl.java:156) ~[undertow-servlet-2.3.18.Final.jar:2.3.18.Final]
        at .springframework.boot.web.embedded.undertow.UndertowServletWebServerFactory.createManager(UndertowServletWebServerFactory.java:331) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.web.embedded.undertow.UndertowServletWebServerFactory.getWebServer(UndertowServletWebServerFactory.java:300) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:188) ~[spring-boot-3.3.5.jar:3.3.5]
        at .springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:162) ~[spring-boot-3.3.5.jar:3.3.5]
        ... 8 common frames omitted

Below is pom.xml, application.properties and configuration class:

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns=".0.0" xmlns:xsi=";
    xsi:schemaLocation=".0.0 .0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.3.5</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.megaheart</groupId>
    <artifactId>mymoney</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>mymoney</name>
    <description>My Money - Help you manage your money effectively</description>
    <url/>
    <licenses>
        <license/>
    </licenses>
    <developers>
        <developer/>
    </developers>
    <scm>
        <connection/>
        <developerConnection/>
        <tag/>
        <url/>
    </scm>
    <properties>
        <java.version>21</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis-reactive</artifactId>
        </dependency>
        <dependency>
            <groupId>.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>.springframework.boot</groupId>
            <artifactId>spring-boot-starter-undertow</artifactId>
        </dependency>
        <dependency>
            <groupId>io.undertow</groupId>
            <artifactId>undertow-servlet</artifactId>
            <version>2.3.18.Final</version>
        </dependency>
        <dependency>
            <groupId>.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>.springframework.restdocs</groupId>
            <artifactId>spring-restdocs-mockmvc</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>.springframework.boot</groupId>
            <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
        </dependency>
        <dependency>
            <groupId>.keycloak</groupId>
            <artifactId>keycloak-admin-client</artifactId>
            <version>25.0.3</version>
        </dependency>
        <dependency>
            <groupId>.keycloak</groupId>
            <artifactId>keycloak-spring-boot-starter</artifactId>
            <version>25.0.3</version>
        </dependency>
        <dependency>
            <groupId>.modelmapper</groupId>
            <artifactId>modelmapper</artifactId>
            <version>3.2.1</version>
        </dependency>
        <dependency>
            <groupId>.springdoc</groupId>
            <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
            <version>2.6.0</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>.asciidoctor</groupId>
                <artifactId>asciidoctor-maven-plugin</artifactId>
                <version>2.2.1</version>
                <executions>
                    <execution>
                        <id>generate-docs</id>
                        <phase>prepare-package</phase>
                        <goals>
                            <goal>process-asciidoc</goal>
                        </goals>
                        <configuration>
                            <backend>html</backend>
                            <doctype>book</doctype>
                        </configuration>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>.springframework.restdocs</groupId>
                        <artifactId>spring-restdocs-asciidoctor</artifactId>
                        <version>${spring-restdocs.version}</version>
                    </dependency>
                </dependencies>
            </plugin>
            <plugin>
                <groupId>.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

application.properties

server.address=0.0.0.0
server.port=6969
spring.application.name=hello
spring.main.allow-bean-definition-overriding=true

# Spring Boot Admin
spring.servlet.multipart.enabled=true
spring.servlet.multipart.file-size-threshold=2KB
spring.servlet.multipart.max-file-size=200MB
spring.servlet.multipart.max-request-size=215MB

# Keycloak configuration
spring.security.oauth2.resourceserver.jwt.issuer-uri=http://localhost:8080/realms/hello_realm

OAuth2ResourceServerSecurityConfiguration.java

@Configuration
@EnableWebSecurity
public class OAuth2ResourceServerSecurityConfiguration {
    @Bean
    SecurityFilterChain resourceServerSecurityFilterChain(
            HttpSecurity http) throws Exception {
        http.oauth2ResourceServer((oauth2) -> oauth2.jwt(Customizer.withDefaults()));

        http.sessionManagement(sessions -> {
            sessions.sessionCreationPolicy(SessionCreationPolicy.STATELESS);
        }).csrf(csrf -> {
            csrf.disable();
        });

        http.authorizeHttpRequests(requests -> {
            requests.requestMatchers("/api/**").authenticated()
                    .anyRequest().permitAll();
        });

        return http.build();
    }
}

Thanks,