# Spring Cloud Security

Spring Cloud Security offers a set of primitives for building secure applications and services with minimum fuss. A declarative model which can be heavily configured externally (or centrally) lends itself to the implementation of large systems of co-operating, remote components, usually with a central indentity management service. It is also extremely easy to use in a service platform like Cloud Foundry. Building on Spring Boot and Spring Security OAuth2 we can quickly create systems that implement common patterns like single sign on, token relay and token exchange.

https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/contributing-docs.adoc

## Quickstart

### OAuth2 Single Sign On

Here’s a Spring Cloud "Hello World" app with HTTP Basic authentication and a single user account:

app.groovy

    @Grab('spring-boot-starter-security')
    @Controller
    class Application {

      @RequestMapping('/')
      String home() {
        'Hello World'
      }

    }

You can run it with `spring run app.groovy` and watch the logs for the password (username is "user"). So far this is just the default for a Spring Boot app.

Here’s a Spring Cloud app with OAuth2 SSO:

app.groovy

    @Controller
    @EnableOAuth2Sso
    class Application {

      @RequestMapping('/')
      String home() {
        'Hello World'
      }

    }

Spot the difference? This app will actually behave exactly the same as the previous one, because it doesn’t know it’s OAuth2 credentals yet.

You can register an app in github quite easily, so try that if you want a production app on your own domain. If you are happy to test on localhost:8080, then set up these properties in your application configuration:

application.yml

    spring:
      oauth2:
        client:
          clientId: bd1c0a783ccdd1c9b9e4
          clientSecret: 1a9030fbca47a5b2c28e92f19050bb77824b5ad1
          accessTokenUri: https://github.com/login/oauth/access_token
          userAuthorizationUri: https://github.com/login/oauth/authorize
          clientAuthenticationScheme: form
        resource:
          userInfoUri: https://api.github.com/user
          preferTokenInfo: false

run the app above and it will redirect to github for authorization. If you are already signed into github you won’t even notice that it has authenticated. These credentials will only work if your app is running on port 8080.

To limit the scope that the client asks for when it obtains an access token you can set `spring.oauth2.client.scope` (comma separated or an array in YAML). By default the scope is empty and it is up to to Authorization Server to decide what the defaults should be, usually depending on the settings in the client registration that it holds.

Note | The examples above are all Groovy scripts. If you want to write the same code in Java (or Groovy) you need to add Spring Security OAuth2 to the classpath (e.g. see the sample here).

### OAuth2 Protected Resource

You want to protect an API resource with an OAuth2 token? Here’s a simple example (paired with the client above):

app.groovy

    @Grab('spring-cloud-starter-security')
    @RestController
    @EnableOAuth2Resource
    class Application {

      @RequestMapping('/')
      def home() {
        [message: 'Hello World']
      }

    }

and

application.yml

    spring:
      oauth2:
        resource:
          userInfoUri: https://api.github.com/user
          preferTokenInfo: false

## More Detail

### Single Sign On

An app will activate `@EnableOAuth2Sso` if you bind provide the following properties in the `Environment`:

- `spring.oauth2.client.*` with `*` equal to `clientId`, `clientSecret`, `accessTokenUri`, `userAuthorizationUri` and one of:

  - `spring.oauth2.resource.userInfoUri` to use the "/me" resource (e.g. "https://uaa.run.pivotal.io/userinfo" on PWS), or

  - `spring.oauth2.resource.tokenInfoUri` to use the token decoding endpoint (e.g. "https://uaa.run.pivotal.io/check_token" on PWS).

  If you specify both the `userInfoUri` and the `tokenInfoUri` then you can set a flag to say that one is preferred over the other (`preferTokenInfo=true` is the default). Or

- `spring.oauth2.resource.jwt.keyValue` to decode a JWT token locally, where the key is a verification key. The verification key value is either a symmetric secret or PEM-encoded RSA public key. If you don’t have the key and it’s public you can provide a URI where it can be downloaded (as a JSON object with a "value" field) with `spring.oauth2.resource.jwt.keyUri`. E.g. on PWS:

      $ curl https://uaa.run.pivotal.io/token_key
      {"alg":"SHA256withRSA","value":"-----BEGIN PUBLIC KEY-----\nMIIBI...\n-----END PUBLIC KEY-----\n"}

Warning | If you use the `spring.oauth2.resource.jwt.keyUri` the authorization server needs to be running when your application starts up. It will log a warning if it can’t find the key, and tell you what to do to fix it.

You can set the preferred scope (as a comma-separated list or YAML array) in `spring.oauth2.client.scope`. It defaults to empty, in which case most Authorization Servers will ask the user for approval for the maximum allowed scope for the client.

There is also a setting for `spring.oauth2.client.clientAuthenticationScheme` which defaults to "header" (but you might need to set it to "form" if, like Github for instance, your OAuth2 provider doesn’t like header authentication). The `spring.oauth2.client.*` properties are bound to an instance of `AuthorizationCodeResourceDetails` so all its properties can be specified.

### Token Type in User Info

Google (and certain other 3rd party identity providers) is 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, but if you need to change it you can set `spring.oauth2.resource.tokenType`.

### Customizing the RestTemplate

The SSO (and Resource Server) features use an `OAuth2RestTemplate` internally to fetch user details for authentication. This is provided as a qualified `@Bean` with id "userInfoRestTemplate", but you shouldn’t need to know that to just use it. The default should be fine for most providers, but occasionally you might need to add additional interceptors, or change the request authenticator (which is how the token gets attached to outgoing requests). To add a customization just create a bean of type `UserInfoRestTemplateCustomizer` - it has a single method that will be called after the bean is created but before it is initialized. The rest template that is being customized here is only used internally to carry out authentication (in the SSO or Resource Server use cases).

A second {@link OAuth2RestTemplate} is available for autowiring if you want to use it for back channel calls, and if there is a token-authenticated user (in a web application) it will have the token injected for you.

Tip

To set an RSA key value in YAML use the "pipe" continuation marker to split it over multiple lines ("|") and remember to indent the key value (it’s a standard YAML language feature). Example:

    oauth2:
      resource:
        jwt:
          keyValue: |
            -----BEGIN PUBLIC KEY-----
            MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKC...
            -----END PUBLIC KEY-----

#### Access Decision Rules

By default the whole application will be secured with OAuth2 with the same access rule ("authenticated"). This includes the Actuator endpoints, which you might prefer to be secured differently, so Spring Cloud Security provides a configurer callback that lets you change the matching and access rules for OAuth2 authentication. Any bean of type `OAuth2SsoConfigurer` (there is a convenient empty base class) will get 2 callbacks, one to set the request matchers for the OAuth2 filter, and one with the full `HttpSecurity` builder (so you can set up all sorts of behaviour, but the main application is to control access rules).

The default login path, i.e. the one that triggers the redirect to the OAuth2 Authorization Server, is "/login". It will always be added to the matching patterns for the OAuth2 SSO, even if you have `OAuth2SsoConfigurer` beans as well. The default logout path is "/logout" and it gets similar treatment, as does the "home" page (which is the logout success page, defaults to "/"). Those paths can be overriden by setting `spring.oauth2.sso.*' (`loginPath`, `logoutPath` and `home.path`).

For example if you want the resources under "/ui/**" to be protected with OAuth2:

    @Configuration
    @EnableOAuth2Sso
    @EnableAutoConfiguration
    protected static class TestConfiguration extends OAuth2SsoConfigurerAdapter {
        @Override
        public void match(RequestMatchers matchers) {
            matchers.antMatchers("/ui/**");
        }
    }

In this case the rest of the application will default to the normal Spring Boot access control (Basic authentication, or whatever custom filters you put in place).

#### Integrating with the Actuator Endpoints

The Spring Boot Actuator endpoints ("/env", "/metrics", etc.) if present will, by default, be protected by the standard Spring Boot basic authentication. The SSO authentication filter is added in a position directly behind the filter that intercepts requests to the Actuator endpoints by default (i.e. `ManagementProperties.BASIC_AUTH_ORDER + 1` which is `Ordered.LOWEST_PRECEDENCE-9` or `2147483636`). If you want to change the order you can set `spring.oauth2.sso.filterOrder`. If you do that and the value is less than the default, then you will need to consider setting the access rules for the Actuator, since they will become accessible to all authenticated users who sign on with the external provider. One way to do that would be to set `management.contextPath=/admin` (for instance) and use an `OAuth2SsoConfigurer` to set the access rules, e.g.

    	@Configuration
    	@EnableOAuth2Sso
    	@EnableAutoConfiguration
    	protected static class TestConfiguration extends OAuth2SsoConfigurerAdapter {
    		@Override
    		public void configure(HttpSecurity http) {
    	         http.authorizeRequests()
                     .antMatchers("/admin/**").role("ADMIN")
                     .anyRequest().authenticated();
    		}
    	}

### Resource Server

The `@EnableOAuth2Resource` annotation will protect your API endpoints if you have the same environment settings as the SSO client, except that it doesn’t need a `tokenUri` or `authorizationUri`, and it also doesn’t need a `clientId` and `clientSecret` if it isn’t using the `tokenInfoUri` (i.e. if it has `jwt.*` or `userInfoUri`).

By default all your endpoints are protected (i.e. "/**") but you can pick and choose by adding a `ResourceServerConfigurerAdapter` (standard Spring OAuth feature), e.g. to protect only the "/api/**" resources

Application.java

    @RestController
    @EnableOAuth2Resource
    class Application extends ResourceServerConfigurerAdapter {

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

      @RequestMapping("/api")
      public String home() {
        return "Hello World";
      }

    }

#### Customizing the JWT Token Converter

When a resource server accepts an access token as a JWT, it has to convert it to an `Authentication` so that Spring Security can do its access decisions. Different token providers might support JWT tokens with different contents, so Spring OAuth2 has an abstraction for converting the token into security domain objects (`AccessTokenConverter`). You can modify the default behaviour easily by providing a `@Bean` of type `JwtAccessTokenConverterConfigurer`, e.g.

    @Component
    public class JwtCustomization extends DefaultAccessTokenConverter implements
            JwtAccessTokenConverterConfigurer {

        @Override
        public void configure(JwtAccessTokenConverter converter) {
            converter.setAccessTokenConverter(this);
        }

        ... // implement custom AccessTokenConverter here

    }

### Token Relay

A Token Relay is where an OAuth2 consumer acts as a Client and forwards the incoming token to outgoing resource requests. The consumer can be a pure Client (like an SSO application) or a Resource Server.

#### Client Token Relay

If your app has a Spring Cloud Zuul embedded reverse proxy (using `@EnableZuulProxy`) then you can ask it to forward OAuth2 access tokens downstream to the services it is proxying. Thus the SSO app above can be enhanced simply like this:

app.groovy

    @Controller
    @EnableOAuth2Sso
    @EnableZuulProxy
    class Application {

    }

and it will (in addition to loggin the user in and grabbing a token) pass the authentication token downstream to the `/proxy/*` services. If those services are implemented with `@EnableOAuth2Resource` then they will get a valid token in the correct header.

How does it work? The `@EnableOAuth2Sso` annotation pulls in `spring-cloud-starter-security` (which you could do manually in a traditional app), and that in turn triggers some autoconfiguration for a `ZuulFilter`, which itself is activated because Zuul is on the classpath (via `@EnableZuulProxy`). The filter just extracts an access token from the currently authenticated user, and puts it in a request header for the downstream requests.

#### Resource Server Token Relay

If your app has `@EnableOAuth2Resource` and also is a Client (i.e. it has a `spring.oauth2.client.clientId`, even if it doesn’t use it), then the `OAuth2RestOperations` that is provided for `@Autowired` users by Spring Cloud (it is declared as `@Primary`) will also forward tokens. If you don’t want to forward tokens (and that is a valid choice, since you might want to act as yourself, rather than the client that sent you the token), then you only need to create your own `OAuth2RestOperations` instead of autowiring the default one. Here’s a basic example showing the use of the autowired rest template ("foo.com" is a Resource Server accepting the same tokens as the surrounding app):

MyController.java

    @Autowired
    private OAuth2RestOperations restTemplate;

    @RequestMapping("/relay")
    public String relay() {
        ResponseEntity<String> response =
          restTemplate.getForEntity("https://foo.com/bar", String.class);
        return "Success! (" + response.getBody() + ")";
    }

## Configuring Authentication Downstream of a Zuul Proxy

You can control the authorization behaviour downstream of an `@EnableZuulProxy` through the `proxy.auth.*` settings. Example:

application.yml

    proxy:
      auth:
        routes:
          customers: oauth2
          stores: passthru
          recommendations: none

In this example the "customers" service gets an OAuth2 token relay, the "stores" service gets a passthrough (the authorization header is just passed downstream), and the "recommendations" service has its authorization header removed. The default behaviour is to do a token relay if there is a token available, and passthru otherwise.

See ProxyAuthenticationProperties for full details.