Similar to other Spring Boot @Enable annotations, you can add the @EnableAuthorizationServer annotation to the class that contains your main method, as the following example shows:

@EnableAuthorizationServer
@SpringBootApplication
public class SimpleAuthorizationServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(SimpleAuthorizationServerApplication, args);
    }
}

Adding this annotation imports other Spring configuration files that add a number of reasonable defaults, such as how tokens ought to be signed, their duration, and what grants to allow.

By spec, numerous OAuth 2.0 endpoints require client authentication, so you need to specify at least one client in order for anyone to be able to communicate with your authorization server.

The following example shows how to specify a client:

security:
  oauth2:
    client:
      client-id: first-client
      client-secret: noonewilleverguess

	Note
	While convenient, this makes a number of assumptions that are unlikely to be viable in production. You likely need to do more than this to ship.

That’s it! But, what do you do with it? We cover that next.

OAuth 2.0 is essentially a framework that specifies strategies for exchanging long-lived tokens for short-lived ones.

By default, @EnableAuthorizationServer grants a client access to client credentials, which means you can do something like the following:

curl first-client:noonewilleverguess@localhost:8080/oauth/token -dgrant_type=client_credentials -dscope=any

The application responds with a token similar to the following:

{
    "access_token" : "f05a1ea7-4c80-4583-a123-dc7a99415588",
    "token_type" : "bearer",
    "expires_in" : 43173,
    "scope" : "any"
}

This token can be presented to any resource server that supports opaque OAuth 2.0 tokens and is configured to point at this authorization server for verification.

From here, you can jump to:

In a typical Spring Boot application secured by Spring Security, users are defined by a UserDetailsService. In that regard, an authorization server is no different, as the following example shows:

@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Bean
    @Override
    public UserDetailsService userDetailsService() {
        return new InMemoryUserDetailsManager(
            User.withDefaultPasswordEncoder()
                .username("enduser")
                .password("password")
                .roles("USER")
                .build());
    }
}

Note that, as is typical of a Spring Security web application, users are defined in a WebSecurityConfigurerAdapter instance.

Incidentally, adding an instance of WebSecurityConfigurerAdapter is all we need for now to add a form login flow for end users. However, note that this is where any other configuration regarding the web application itself, not the OAuth 2.0 API, goes.

If you want to customize the login page, offer more than just form login for the user, or add additional support like password recovery, the WebSecurityConfigurerAdapter picks it up.

OAuth2 Boot does not support configuring a redirect URI as a property — say, alongside client-id and client-secret.

To add a redirect URI, you need to specify the client by using either InMemoryClientDetailsService or JdbcClientDetailsService.

Doing either means replacing the OAuth2 Boot-provided AuthorizationServerConfigurer with your own, as the following example shows:

@Configuration
public class AuthorizationServerConfig extends AuthorizationServerConfigurerAdapter {

    @Bean
    PasswordEncoder passwordEncoder() {
        return PasswordEncoderFactories.createDelegatingPasswordEncoder();
    }

    protected void configure(ClientDetailsServiceConfigurer clients) {
        clients
            .inMemory()
                .withClient("first-client")
                .secret(passwordEncoder().encode("noonewilleverguess"))
                .scopes("resource:read")
                .authorizedGrantTypes("authorization_code")
                .redirectUris("http://localhost:8081/oauth/login/client-app");
    }
}

Testing OAuth can be tricky since it requires more than one server to see the full flow in action. However, the first steps are straight-forward:

The flow could continue at this point by standing up any resource server that is configured for opaque tokens and is pointed at this authorization server instance.

End users are specified in a WebSecurityConfigurerAdapter through a UserDetailsService. So, if you use the OAuth2 Boot defaults (meaning you haven’t implemented a AuthorizationServerConfigurer), you can expose a UserDetailsService and be done, as the following example shows:

@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired DataSource dataSource;

    @Bean
    @Override
    public UserDetailsService userDetailsService() {
        return new JdbcUserDetailsManager(this.dataSource);
    }
}

In case you need to do more specialized configuration of the AuthenticationManager, you can do so in the WebSecurityConfigurerAdapter and then expose it, as the following example shows:

@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Bean(BeansId.AUTHENTICATION_MANAGER)
    @Override
    public AuthenticationManager authenticationManagerBean() {
        return super.authenticationManagerBean();
    }

    @Override
    protected void configure(AuthenticationManagerBuilder auth) {
        auth.authenticationProvider(customAuthenticationProvider());
    }
}

If you use the OAuth2 Boot defaults, then it picks up the bean automatically.

Any configured AuthenticationManager is available in AuthenticationConfiguration. This means that, if you need to have an AuthorizationServerConfigurer (in which case you need to do your own autowiring), you can have it depend on AuthenticationConfiguration to get the AuthenticationManager bean, as the following class shows:

@Component
public class CustomAuthorizationServerConfigurer extends
    AuthorizationServerConfigurerAdapter {

    AuthenticationManager authenticationManager;

    public CustomAuthorizationServerConfigurer(AuthenticationConfiguration authenticationConfiguration) {
        this.authenticationManager = authenticationConfiguration.getAuthenticationManager();
    }

    @Override
    public void configure(ClientDetailsServiceConfigurer clients) {
        // .. your client configuration that allows the password grant
    }

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) {
        endpoints.authenticationManager(authenticationManager);
    }
}

@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Bean
    @Override
    public UserDetailsService userDetailsService() {
        return new MyCustomUserDetailsService();
    }
}

In the most sophisticated case, where the AuthenticationManager needs special configuration and you have your own AuthenticationServerConfigurer, then you need to both create your own AuthorizationServerConfigurerAdapter and your own WebSecurityConfigurerAdapter:

@Component
public class CustomAuthorizationServerConfigurer extends
    AuthorizationServerConfigurerAdapter {

    AuthenticationManager authenticationManager;

    public CustomAuthorizationServerConfigurer(AuthenticationManager authenticationManager) {
        this.authenticationManager = authenticationManager;
    }

    @Override
    public void configure(ClientDetailsServiceConfigurer clients) {
        // .. your client configuration that allows the password grant
    }

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) {
        endpoints.authenticationManager(authenticationManager);
    }
}

@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Bean(BeansId.AUTHENTICATION_MANAGER)
    @Override
    public AuthenticationManager authenticationManagerBean() {
        return super.authenticationManagerBean();
    }

    @Override
    protected void configure(AuthenticationManagerBuilder auth) {
        auth.authenticationProvider(customAuthenticationProvider());
    }
}

To change the format used for access and refresh tokens, you can change out the AccessTokenConverter and the TokenStore, as the following example shows:

@EnableAuthorizationServer
@Configuration
public class JwkSetConfiguration extends AuthorizationServerConfigurerAdapter {

	AuthenticationManager authenticationManager;
	KeyPair keyPair;

	public JwkSetConfiguration(AuthenticationConfiguration authenticationConfiguration,
			KeyPair keyPair) throws Exception {

		this.authenticationManager = authenticationConfiguration.getAuthenticationManager();
		this.keyPair = keyPair;
	}

    // ... client configuration, etc.

	@Override
	public void configure(AuthorizationServerEndpointsConfigurer endpoints) {
		// @formatter:off
		endpoints
			.authenticationManager(this.authenticationManager)
			.accessTokenConverter(accessTokenConverter())
			.tokenStore(tokenStore());
		// @formatter:on
	}

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

	@Bean
	public JwtAccessTokenConverter accessTokenConverter() {
		JwtAccessTokenConverter converter = new JwtAccessTokenConverter();
		converter.setKeyPair(this.keyPair);
		return converter;
	}
}

Spring Security OAuth does not support JWKs, nor does @EnableAuthorizationServer support adding more OAuth 2.0 API endpoints to its initial set. However, we can add this with only a few lines.

First, you need to add another dependency: com.nimbusds:nimbus-jose-jwt. This gives you the appropriate JWK primitives.

Second, instead of using @EnableAuthorizationServer, you need to directlyu include its two @Configuration classes:

@FrameworkEndpoint
class JwkSetEndpoint {
	KeyPair keyPair;

	public JwkSetEndpoint(KeyPair keyPair) {
		this.keyPair = keyPair;
	}

	@GetMapping("/.well-known/jwks.json")
	@ResponseBody
	public Map<String, Object> getKey(Principal principal) {
		RSAPublicKey publicKey = (RSAPublicKey) this.keyPair.getPublic();
		RSAKey key = new RSAKey.Builder(publicKey).build();
		return new JWKSet(key).toJSONObject();
	}
}

@Configuration
class JwkSetEndpointConfiguration extends AuthorizationServerSecurityConfiguration {
	@Override
	protected void configure(HttpSecurity http) throws Exception {
		super.configure(http);
		http
			.requestMatchers()
				.mvcMatchers("/.well-known/jwks.json")
				.and()
			.authorizeRequests()
				.mvcMatchers("/.well-known/jwks.json").permitAll();
	}
}

Then, since you do not need to change AuthorizationServerEndpointsConfiguration, you can @Import it instead of using @EnableAuthorizationServer, as the following example shows:

@Import(AuthorizationServerEndpointsConfiguration.class)
@Configuration
public class JwkSetConfiguration extends AuthorizationServerConfigurerAdapter {

    // ... the rest of the configuration from the previous section
}

Now you can POST to the /oauth/token endpoint (as before) to obtain a token and then present that to a Spring Security 5.1 Resource Server.

Similar to other Spring Boot @Enable annotations, you can add the @EnableResourceServer annotation to the class that contains your main method, as the following example shows:

@EnableResourceServer
@SpringBootApplication
public class SimpleAuthorizationServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(SimpleAuthorizationServerApplication, args);
    }
}

Adding this annotation adds the OAuth2AuthenticationProcessingFilter, though it will need one more configuration to know how to appropriately process and validate tokens.

Bearer Tokens typically come in one of two forms: JWT-encoded or opaque. You will need to configure the resource server with one or the other strategy.

security:
  oauth2:
    resource:
      jwk:
        key-set-uri: https://idp.example.com/.well-known/jwks.json

Opaque

To indicate opaque, simply specify the Authorization Server endpoint that knows how to decode the token:

security:
  oauth2:
    resource:
      token-info-uri: https://idp.example.com/oauth2/introspect

	Note
	It’s likely this endpoint requires some kind of authorization separate from the token itself, for example, client authentication.

That’s it! But, what do you do with it? We cover that next.

To confirm that Resource Server is correctly processing tokens, you can add a simple controller endpoint like so:

@RestController
public class SimpleController
	@GetMapping("/whoami")
	public String whoami(@AuthenticationPrincipal(expression="name") String name) {
		return name;
    }
}

Then, obtain an active access token from your Authorization Server and present it to the Resource Server:

curl -H "Authorization: $TOKEN" http://localhost:8080/whoami

And you should see the value of the user_name attribute in the token.

From this point, you may want to learn more about three alternative ways to authenticate using bearer tokens:

Internally, Resource Server uses an OAuth2RestTemplate to invoke the /userinfo endpoint. At times, it may be necessary to add filters or perform other customization for this invocation. To customize the creation of this bean, you can expose a UserInfoRestTemplateCustomizer, like so:

@Bean
public UserInfoRestTemplateCustomizer customHeader() {
	return restTemplate ->
			restTemplate.getInterceptors().add(new MyCustomInterceptor());
}

This bean will be handed to a UserInfoTemplateFactory which will add other configurations helpful to coordinating with the /userinfo endpoint.

And, of course, you can replace the UserInfoTemplateFactory completely, if you need complete control over `OAuth2RestTemplate’s configuration.

Google and certain other third-party identity providers are more strict about the token type name that is sent in the headers to the user info endpoint. The default is Bearer, which suits most providers and matches the spec. However, if you need to change it, you can set security.oauth2.resource.token-type.

OAuth2 resources are protected by a filter chain with the order specified by security.oauth2.resource.filter-order.

By default the filters in AuthorizationServerConfigurerAdapter come first, followed by those in ResourceServerConfigurerAdapter, followed by those in WebSecurityConfigurerAdapter.

This means that all application endpoints will require bearer token authentication unless one of two things happens:

The first, changing the filter chain order, can be done by moving WebSecurityConfigurerAdapter in front of ResourceServerConfigurerAdapter like so:

@Order(2)
@EnableWebSecurity
public WebSecurityConfig extends WebSecurityConfigurerAdapter {
	// ...
}

	Note
	Resource Server’s default @Order value is 3 which is why the example sets Web’s @Order to 2, so that it’s evaluated earlier.

While this may work, it’s a little odd since we may simply trade one problem:

For another:

The more robust solution, then, is to indicate to ResourceServerConfigurerAdapter which endpoints should be secured by bearer token authentication.

For example, the following configures Resource Server to secure the web application endpoints that begin with /rest:

@EnableResourceServer
public ResourceServerConfig extends ResourceServerConfigurerAdapter {
	@Override
    protected void configure(HttpSecurity http) {
        http
            .requestMatchers()
                .antMatchers("/rest/**")
            .authorizeRequests()
                .anyRequest().authenticated();
    }
}

Resource Server, when also configured as a client, may rely on a request-scoped OAuth2ClientContext bean during the authentication process. And, in some error situations, Resource Server forwards to the ERROR servlet dispatcher.

By default, request-scoped beans aren’t available in the ERROR dispatch. And, because of this, you may see a complaint about the OAuth2ClientContext bean not being available.

The simplest approach may be to permit the /error endpoint, so that Resource Server doesn’t try and authenticate the request:

public class PermitErrorConfig extends ResourceServerConfigurerAdapter {
    @Override
	public void configure(HttpSecurity http) throws Exception {
		// @formatter:off
		http
			.authorizeRequests()
				.antMatchers("/error").permitAll()
				.anyRequest().authenticated();
		// @formatter:on
	}
}

Other solutions are to configure Spring so that the RequestContextFilter is registered with the error dispatch or to register a RequestContextListener bean.