api-gateway에 연결하는 방법을 선택했다.
먼저 config 파일을 하나 만들어준다.

KeycloakConfig

package gabia.library.config;

import org.keycloak.adapters.KeycloakConfigResolver;
import org.keycloak.adapters.KeycloakDeployment;
import org.keycloak.adapters.KeycloakDeploymentBuilder;
import org.keycloak.adapters.spi.HttpFacade;
import org.keycloak.adapters.springsecurity.authentication.KeycloakAuthenticationProvider;
import org.keycloak.adapters.springsecurity.config.KeycloakWebSecurityConfigurerAdapter;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.core.authority.mapping.SimpleAuthorityMapper;
import org.springframework.security.core.session.SessionRegistryImpl;
import org.springframework.security.web.authentication.session.RegisterSessionAuthenticationStrategy;
import org.springframework.security.web.authentication.session.SessionAuthenticationStrategy;

import java.io.InputStream;

@Configuration
@EnableWebSecurity
public class KeycloakConfig extends KeycloakWebSecurityConfigurerAdapter {
    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
        KeycloakAuthenticationProvider keycloakAuthenticationProvider = keycloakAuthenticationProvider();
        keycloakAuthenticationProvider.setGrantedAuthoritiesMapper(new SimpleAuthorityMapper());
        auth.authenticationProvider(keycloakAuthenticationProvider);
    }
    @Bean
    @Override
    protected SessionAuthenticationStrategy sessionAuthenticationStrategy() {
        return new RegisterSessionAuthenticationStrategy(
                new SessionRegistryImpl());
    }
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        super.configure(http);
        http.authorizeRequests()
                .antMatchers("/app*").permitAll()
                .antMatchers("/book-service/*").hasRole("ADMIN") //여기서 말하는 Role은
                .antMatchers("/user-service/*").hasRole("USER") //realm의 role을 말함
                .anyRequest().authenticated();
    }
    @Bean
    public KeycloakConfigResolver keycloakConfigResolver() {
        return new KeycloakConfigResolver() {
            private KeycloakDeployment keycloakDeployment;
            @Override
            public KeycloakDeployment resolve(HttpFacade.Request facade) {
                if (keycloakDeployment != null) {
                    return keycloakDeployment;
                }
                InputStream configInputStream = getClass().getResourceAsStream("/keycloak.json");
                return KeycloakDeploymentBuilder.build(configInputStream);
            }
        };
    }
}

keycloak.json

{
  "realm": "MSA", //realm 이름
  "auth-server-url": "http://localhost:8080/auth/",
  "ssl-required": "external",
  "resource": "memberService", //client 이름
  "credentials": {
    "secret": "영어로 되어있는 클라이언트 비번 쳐주시면 됩니당" //client 비번
  },
  "confidential-port": 0
}

build.gradle

keycloak 관련 해서 불러올 수 있도록 추가해준다

version = '0.0.1-SNAPSHOT'

ext['springCloudVersion'] = 'Hoxton.RELEASE'

jar {
    manifest {
        attributes 'Main-Class': 'gabia.library.ApigatewayApplication'
    }
}

dependencies {
    implementation project(':common')
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation('org.springframework.cloud:spring-cloud-starter-netflix-zuul')
    implementation('org.springframework.cloud:spring-cloud-starter-netflix-eureka-client')
    implementation('org.springframework.boot:spring-boot-starter-security')
    implementation('org.keycloak:keycloak-spring-boot-starter') //추가한 행
    implementation group: 'io.jsonwebtoken', name: 'jjwt', version: '0.9.1'
    implementation group: 'io.springfox', name: 'springfox-swagger-ui', version: '2.9.2'
    testImplementation('org.springframework.boot:spring-boot-starter-test') {
        exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
    }
}

dependencyManagement {
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
        mavenBom "org.keycloak.bom:keycloak-adapter-bom:12.0.1" //추가한 행
    }
}

test {
    useJUnitPlatform()
}

이렇게 두개의 keycloak관련한 의존성을 주입해주어야
keycloakConfig에서 keycloak 관련 jar들이 성공적으로 import된다.