<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.security.oauth.boot</groupId>
    <artifactId>spring-security-oauth2-autoconfigure</artifactId>
</dependency>

@Configuration
@EnableAuthorizationServer
public class AuthorizationServerConfig extends AuthorizationServerConfigurerAdapter {

    @Autowired
    private AuthenticationManager authenticationManager;

    @Autowired
    private UserDetailsService userDetailsService;

    @Bean
    public TokenStore tokenStore() {
        return new InMemoryTokenStore();
    }

    @Bean
    public DefaultTokenServices tokenServices() {
        DefaultTokenServices tokenServices = new DefaultTokenServices();
        tokenServices.setTokenStore(tokenStore());
        tokenServices.setSupportRefreshToken(true);
        tokenServices.setAccessTokenValiditySeconds(60 * 60);
        tokenServices.setRefreshTokenValiditySeconds(60 * 60 * 24);
        return tokenServices;
    }

    @Override
    public void configure(ClientDetailsServiceConfigurer clients) throws Exception {
        clients.inMemory()
                .withClient("client")
                .secret("secret")
                .authorizedGrantTypes("password", "refresh_token")
                .scopes("read", "write")
                .accessTokenValiditySeconds(60 * 60)
                .refreshTokenValiditySeconds(60 * 60 * 24);
    }

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {
        endpoints.tokenStore(tokenStore())
                .tokenServices(tokenServices())
                .authenticationManager(authenticationManager)
                .userDetailsService(userDetailsService);
    }
}

@Configuration
@EnableResourceServer
public class ResourceServerConfig extends ResourceServerConfigurerAdapter {

    @Override
    public void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests()
                .antMatchers("/api/**").authenticated()
                .anyRequest().permitAll();
    }
}

@Configuration
@EnableOAuth2Client
public class OAuth2ClientConfig {

    @Bean
    public OAuth2ProtectedResourceDetails clientCredentialsResourceDetails() {
        ClientCredentialsResourceDetails details = new ClientCredentialsResourceDetails();
        details.setAccessTokenUri("http://localhost:8080/oauth/token");
        details.setClientId("client");
        details.setClientSecret("secret");
        details.setGrantType("client_credentials");
        details.setScope(Arrays.asList("read", "write"));
        return details;
    }

    @Bean
    public RestTemplate restTemplate(OAuth2ClientContext oauth2ClientContext) {
        return new OAuth2RestTemplate(clientCredentialsResourceDetails(), oauth2ClientContext);
    }
}

@RestController
@RequestMapping("/api")
public class ApiController {

    @Autowired
    private RestTemplate restTemplate;

    @GetMapping("/hello")
    public String hello() {
        ResponseEntity<String> response = restTemplate.getForEntity("http://localhost:8080/hello", String.class);
        return response.getBody();
    }
}