<dependency>
    <groupId>org.springframework.security.oauth</groupId>
    <artifactId>spring-security-oauth2</artifactId>
    <version>2.4.0</version>
</dependency>

@Configuration
@EnableAuthorizationServer
public class AuthorizationServerConfig extends AuthorizationServerConfigurerAdapter {

    @Autowired
    private AuthenticationManager authenticationManager;

    @Override
    public void configure(ClientDetailsServiceConfigurer clients) throws Exception {
        clients.inMemory()
                .withClient("client")
                .secret("{noop}secret")
                .authorizedGrantTypes("authorization_code")
                .scopes("read", "write")
                .redirectUris("http://localhost:8080/callback");
    }

    @Override
    public void configure(AuthorizationServerEndpoints endpoints) throws Exception {
    endpoints.authenticationManager(authenticationManager);
}
}

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

@Override
public void configure(ResourceServerSecurityConfigurer resources) throws Exception {
    resources.resourceId("resource");
}
}

security:
oauth2:
client:
clientId: client
clientSecret: secret
accessTokenUri: http://localhost:8080/oauth/token
userAuthorizationUri: http://localhost:8080/oauth/authorize
scope: read,write
redirectUri: http://localhost:8080/callback

@GetMapping("/qrcode")
public ResponseEntity<byte[]> getQRCode() throws IOException, WriterException {
String codeUrl = "http://localhost:8080/oauth/authorize?response_type=code&client_id=client&redirect_uri=http://localhost:8080/callback";
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
BitMatrix bitMatrix = new MultiFormatWriter().encode(codeUrl, BarcodeFormat.QR_CODE, 200, 200);
MatrixToImageWriter.writeToStream(bitMatrix, "png", outputStream);
return ResponseEntity.ok().contentType(MediaType.IMAGE_PNG).body(outputStream.toByteArray());
}

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        registry.addHandler(new QRCodeHandler(), "/qrcodeHandler");
    }

    class QRCodeHandler extends TextWebSocketHandler {

        private final Map<String, WebSocketSession> sessions = new ConcurrentHashMap<>();

        @Override
        public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
            String token = message.getPayload();
            if (sessions.containsKey(token)) {
                WebSocketSession clientSession = sessions.get(token);
                clientSession.sendMessage(new TextMessage("authenticated"));
                session.sendMessage(new TextMessage("authenticated"));
            } else {
                sessions.put(token, session);
            }
        }

        @Override
        public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
            sessions.values().remove(session);
        }
    }
}

@Controller
public class CallbackController {

    @Autowired
    private OAuth2RestTemplate restTemplate;

    @GetMapping("/callback")
    public String callback(@RequestParam("code") String code) {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
        MultiValueMap<String, String> params = new LinkedMultiValueMap<>();
        params.add("grant_type", "authorization_code");
        params.add("code", code);
        params.add("redirect_uri", "http://localhost:8080/callback");
        params.add("client_id", "client");
        params.add("client_secret", "secret");
        HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(params, headers);
        OAuth2AccessToken token = restTemplate.postForObject("http://localhost:8080/oauth/token", request, OAuth2AccessToken.class);
        return "redirect:/home";
    }
}