19. OAuth2 WebFlux

Spring Security provides OAuth2 and WebFlux integration for reactive applications.

19.1 OAuth 2.0 Login

The OAuth 2.0 Login feature provides an application with the capability to have users log in to the application by using their existing account at an OAuth 2.0 Provider (e.g. GitHub) or OpenID Connect 1.0 Provider (such as Google). OAuth 2.0 Login implements the use cases: "Login with Google" or "Login with GitHub".

Note

OAuth 2.0 Login is implemented by using the Authorization Code Grant , as specified in the OAuth 2.0 Authorization Framework and OpenID Connect Core 1.0.

19.1.1 Spring Boot 2.0 Sample

Spring Boot 2.0 brings full auto-configuration capabilities for OAuth 2.0 Login.

This section shows how to configure the OAuth 2.0 Login WebFlux sample using Google as the Authentication Provider and covers the following topics:

Initial setup

To use Google’s OAuth 2.0 authentication system for login, you must set up a project in the Google API Console to obtain OAuth 2.0 credentials.

Note

Google’s OAuth 2.0 implementation for authentication conforms to the OpenID Connect 1.0 specification and is OpenID Certified.

Follow the instructions on the OpenID Connect page, starting in the section, "Setting up OAuth 2.0".

After completing the "Obtain OAuth 2.0 credentials" instructions, you should have a new OAuth Client with credentials consisting of a Client ID and a Client Secret.

Setting the redirect URI

The redirect URI is the path in the application that the end-user’s user-agent is redirected back to after they have authenticated with Google and have granted access to the OAuth Client (created in the previous step) on the Consent page.

In the "Set a redirect URI" sub-section, ensure that the Authorized redirect URIs field is set to http://localhost:8080/login/oauth2/code/google .

Tip

The default redirect URI template is {baseUrl}/login/oauth2/code/{registrationId} . The registrationId is a unique identifier for the ClientRegistration. For our example, the registrationId is google .

Configure application.yml

Now that you have a new OAuth Client with Google, you need to configure the application to use the OAuth Client for the authentication flow . To do so:

  • Go to application.yml and set the following configuration:
spring:
  security:
    oauth2:
      client:
        registration:   (1)
          google:   (2)
            client-id: google-client-id
            client-secret: google-client-secret

Example 19.1. OAuth Client properties

  • (1) spring.security.oauth2.client.registration is the base property prefix for OAuth Client properties.

  • (2) Following the base property prefix is the ID for the ClientRegistration, such as google.

  • Replace the values in the client-id and client-secret property with the OAuth 2.0 credentials you created earlier.

Boot up the application

Launch the Spring Boot 2.0 sample and go to http://localhost:8080 . You are then redirected to the default auto-generated login page, which displays a link for Google.

Click on the Google link, and you are then redirected to Google for authentication.

After authenticating with your Google account credentials, the next page presented to you is the Consent screen. The Consent screen asks you to either allow or deny access to the OAuth Client you created earlier. Click Allow to authorize the OAuth Client to access your email address and basic profile information.

At this point, the OAuth Client retrieves your email address and basic profile information from the UserInfo Endpoint and establishes an authenticated session.

19.1.2 Using OpenID Provider Configuration

For well known providers, Spring Security provides the necessary defaults for the OAuth Authorization Provider’s configuration. If you are working with your own Authorization Provider that supports OpenID Provider Configuration, you may use the OpenID Provider Configuration Response the issuer-uri can be used to configure the application.

spring:
  security:
    oauth2:
      client:
        provider:
          keycloak:
            issuer-uri: https://idp.example.com/auth/realms/demo
        registration:
          keycloak:
            client-id: spring-security
            client-secret: 6cea952f-10d0-4d00-ac79-cc865820dc2c

The issuer-uri instructs Spring Security to leverage the endpoint at https://idp.example.com/auth/realms/demo/.well-known/openid-configuration to discover the configuration. The client-id and client-secret are linked to the provider because keycloak is used for both the provider and the registration.

19.1.3 Explicit OAuth2 Login Configuration

A minimal OAuth2 Login configuration is shown below:

@Bean
ReactiveClientRegistrationRepository clientRegistrations() {
    ClientRegistration clientRegistration = ClientRegistrations
            .fromOidcIssuerLocation("https://idp.example.com/auth/realms/demo")
            .clientId("spring-security")
            .clientSecret("6cea952f-10d0-4d00-ac79-cc865820dc2c")
            .build();
    return new InMemoryReactiveClientRegistrationRepository(clientRegistration);
}

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        // ...
        .oauth2Login();
    return http.build();
}

Additional configuration options can be seen below:

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        // ...
        .oauth2Login()
            .authenticationConverter(converter)
            .authenticationManager(manager)
            .authorizedClientRepository(authorizedClients)
            .clientRegistrationRepository(clientRegistrations);
    return http.build();
}

19.2 OAuth2 Client

Spring Security’s OAuth Support allows obtaining an access token without authenticating. A basic configuration with Spring Boot can be seen below:

spring:
  security:
    oauth2:
      client:
        registration:
          github:
            client-id: replace-with-client-id
            client-secret: replace-with-client-secret
            scopes: read:user,public_repo

You will need to replace the client-id and client-secret with values registered with GitHub.

The next step is to instruct Spring Security that you wish to act as an OAuth2 Client so that you can obtain an access token.

@Bean
SecurityWebFilterChain configure(ServerHttpSecurity http) throws Exception {
    http
        // ...
        .oauth2Client();
    return http.build();
}

You can now leverage Spring Security’s Chapter 21, WebClient or @RegisteredOAuth2AuthorizedClient support to obtain and use the access token.

19.3 OAuth2 Resource Server

Spring Security supports protecting endpoints using JWT-encoded OAuth 2.0 Bearer Tokens.

This is handy in circumstances where an application has federated its authority management out to an authorization server (for example, Okta or Ping Identity). This authorization server can be consulted by Resource Servers to validate authority when serving requests.

Note

A complete working example can be found in OAuth 2.0 Resource Server WebFlux sample.

19.3.1 Dependencies

Most Resource Server support is collected into spring-security-oauth2-resource-server . However, the support for decoding and verifying JWTs is in spring-security-oauth2-jose , meaning that both are necessary in order to have a working resource server that supports JWT-encoded Bearer Tokens.

19.3.2 Minimal Configuration

When using Spring Boot, configuring an application as a resource server consists of two basic steps. First, include the needed dependencies and second, indicate the location of the authorization server.

Specify the Authorization Server

In a Spring Boot application, to specify which authorization server to use, simply do:

spring:
  security:
    oauth2:
      resourceserver:
        jwt:
          issuer-uri: https://idp.example.com

Where https://idp.example.com is the value contained in the iss claim for JWT tokens that the authorization server will issue. Resource Server will use this property to further self-configure, discover the authorization server’s public keys, and subsequently validate incoming JWTs.

Note

To use the issuer-uri property, it must also be true that https://idp.example.com/.well-known/openid-configuration is a supported endpoint for the authorization server. This endpoint is referred to as a Provider Configuration endpoint.

And that’s it!

Startup Expectations

When this property and these dependencies are used, Resource Server will automatically configure itself to validate JWT-encoded Bearer Tokens.

It achieves this through a deterministic startup process:

  • Hit the Provider Configuration endpoint, https://the.issuer.location/.well-known/openid-configuration , processing the response for the jwks_url property

  • Configure the validation strategy to query jwks_url for valid public keys

  • Configure the validation strategy to validate each JWTs iss claim against https://idp.example.com .

A consequence of this process is that the authorization server must be up and receiving requests in order for Resource Server to successfully start up.

Note

If the authorization server is down when Resource Server queries it (given appropriate timeouts), then startup will fail.

Runtime Expectations

Once the application is started up, Resource Server will attempt to process any request containing an Authorization: Bearer header:

GET / HTTP/1.1
Authorization: Bearer some-token-value # Resource Server will process this

So long as this scheme is indicated, Resource Server will attempt to process the request according to the Bearer Token specification.

Given a well-formed JWT token, Resource Server will:

  • Validate its signature against a public key obtained from the jwks_url endpoint during startup and matched against the JWTs header

  • Validate the JWTs exp and nbf timestamps and the JWTs iss claim, and

  • Map each scope to an authority with the prefix SCOPE_ .

Note

As the authorization server makes available new keys, Spring Security will automatically rotate the keys used to validate the JWT tokens.

The resulting Authentication#getPrincipal , by default, is a Spring Security Jwt object, and Authentication#getName maps to the JWT’s sub property, if one is present.

How to Configure without Tying Resource Server startup to an authorization server’s availability

How to Configure without Spring Boot

Specifying the Authorization Server JWK Set Uri Directly

If the authorization server doesn’t support the Provider Configuration endpoint, or if Resource Server must be able to start up independently from the authorization server, then issuer-uri can be exchanged for jwk-set-uri :

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

Note

The JWK Set uri is not standardized, but can typically be found in the authorization server’s documentation

Consequently, Resource Server will not ping the authorization server at startup. However, it will also no longer validate the iss claim in the JWT (since Resource Server no longer knows what the issuer value should be).

Note

This property can also be supplied directly on the DSL.

Overriding or Replacing Boot Auto Configuration

There are two @Bean s that Spring Boot generates on Resource Server’s behalf.

The first is a SecurityWebFilterChain that configures the app as a resource server:

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        .authorizeExchange()
            .anyExchange().authenticated()
            .and()
        .oauth2ResourceServer()
            .jwt();
    return http.build();
}

If the application doesn’t expose a SecurityWebFilterChain bean, then Spring Boot will expose the above default one.

Replacing this is as simple as exposing the bean within the application:

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        .authorizeExchange()
            .pathMatchers("/message/**").hasAuthority("SCOPE_message:read")
            .anyExchange().authenticated()
            .and()
        .oauth2ResourceServer()
            .jwt();
    return http.build();
}

The above requires the scope of message:read for any URL that starts with /messages/ .

Methods on the oauth2ResourceServer DSL will also override or replace auto configuration.

For example, the second @Bean Spring Boot creates is a ReactiveJwtDecoder , which decodes String tokens into validated instances of Jwt :

@Bean
public ReactiveJwtDecoder jwtDecoder() {
    return ReactiveJwtDecoders.fromOidcIssuerLocation(issuerUri);
}

If the application doesn’t expose a ReactiveJwtDecoder bean, then Spring Boot will expose the above default one.

And its configuration can be overridden using jwkSetUri() or replaced using decoder() .

Using jwkSetUri()

An authorization server’s JWK Set Uri can be configured as a configuration property or it can be supplied in the DSL:

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        .authorizeExchange()
            .anyExchange().authenticated()
            .and()
        .oauth2ResourceServer()
            .jwt()
                .jwkSetUri("https://idp.example.com/.well-known/jwks.json");
    return http.build();
}

Using jwkSetUri() takes precedence over any configuration property.

Using decoder()

More powerful than jwkSetUri() is decoder() , which will completely replace any Boot auto configuration of JwtDecoder :

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        .authorizeExchange()
            .anyExchange().authenticated()
            .and()
        .oauth2ResourceServer()
            .jwt()
                .decoder(myCustomDecoder());
    return http.build();
}

This is handy when deeper configuration, like validation, is necessary.

Exposing a ReactiveJwtDecoder @Bean

Or, exposing a ReactiveJwtDecoder @Bean has the same effect as decoder() :

@Bean
public JwtDecoder jwtDecoder() {
    return new NimbusReactiveJwtDecoder(jwkSetUri);
}

Configuring Authorization

A JWT that is issued from an OAuth 2.0 Authorization Server will typically either have a scope or scp attribute, indicating the scopes (or authorities) it’s been granted, for example:

{ …, "scope" : "messages contacts"}

When this is the case, Resource Server will attempt to coerce these scopes into a list of granted authorities, prefixing each scope with the string "SCOPE_".

This means that to protect an endpoint or method with a scope derived from a JWT, the corresponding expressions should include this prefix:

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        .authorizeExchange()
            .mvcMatchers("/contacts/**").hasAuthority("SCOPE_contacts")
            .mvcMatchers("/messages/**").hasAuthority("SCOPE_messages")
            .anyExchange().authenticated()
            .and()
        .oauth2ResourceServer()
            .jwt();
    return http.build();
}

Or similarly with method security:

@PreAuthorize("hasAuthority('SCOPE_messages')")
public List<Message> getMessages(...) {}
Extracting Authorities Manually

However, there are a number of circumstances where this default is insufficient. For example, some authorization servers don’t use the scope attribute, but instead have their own custom attribute. Or, at other times, the resource server may need to adapt the attribute or a composition of attributes into internalized authorities.

To this end, the DSL exposes jwtAuthenticationConverter() :

@Bean
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    http
        .authorizeExchange()
            .anyExchange().authenticated()
            .and()
        .oauth2ResourceServer()
            .jwt()
                .jwtAuthenticationConverter(grantedAuthoritiesExtractor());
    return http.build();
}

Converter<Jwt, Mono<AbstractAuthenticationToken>> grantedAuthoritiesExtractor() {
    GrantedAuthoritiesExtractor extractor = new GrantedAuthoritiesExtractor();
    return new ReactiveJwtAuthenticationConverterAdapter(extractor);
}

which is responsible for converting a Jwt into an Authentication .

We can override this quite simply to alter the way granted authorities are derived:

static class GrantedAuthoritiesExtractor extends JwtAuthenticationConverter {
    protected Collection<GrantedAuthorities> extractAuthorities(Jwt jwt) {
        Collection<String> authorities = (Collection<String>)
                jwt.getClaims().get("mycustomclaim");

        return authorities.stream()
                .map(SimpleGrantedAuthority::new)
                .collect(Collectors.toList());
    }
}

For more flexibility, the DSL supports entirely replacing the converter with any class that implements Converter<Jwt, Mono<AbstractAuthenticationToken>> :

static class CustomAuthenticationConverter implements Converter<Jwt, Mono<AbstractAuthenticationToken>> {
    public AbstractAuthenticationToken convert(Jwt jwt) {
        return Mono.just(jwt).map(this::doConversion);
    }
}

Configuring Validation

Using minimal Spring Boot configuration, indicating the authorization server’s issuer uri, Resource Server will default to verifying the iss claim as well as the exp and nbf timestamp claims.

In circumstances where validation needs to be customized, Resource Server ships with two standard validators and also accepts custom OAuth2TokenValidator instances.

Customizing Timestamp Validation

JWT’s typically have a window of validity, with the start of the window indicated in the nbf claim and the end indicated in the exp claim.

However, every server can experience clock drift, which can cause tokens to appear expired to one server, but not to another. This can cause some implementation heartburn as the number of collaborating servers increases in a distributed system.

Resource Server uses JwtTimestampValidator to verify a token’s validity window, and it can be configured with a clockSkew to alleviate the above problem:

@Bean
ReactiveJwtDecoder jwtDecoder() {
     NimbusReactiveJwtDecoder jwtDecoder = (NimbusReactiveJwtDecoder)
             ReactiveJwtDecoders.withOidcIssuerLocation(issuerUri);

     OAuth2TokenValidator<Jwt> withClockSkew = new DelegatingOAuth2TokenValidator<>(
            new JwtTimestampValidator(Duration.ofSeconds(60)),
            new IssuerValidator(issuerUri));

     jwtDecoder.setJwtValidator(withClockSkew);

     return jwtDecoder;
}

Note

By default, Resource Server configures a clock skew of 30 seconds.

Configuring a Custom Validator

Adding a check for the aud claim is simple with the OAuth2TokenValidator API:

public class AudienceValidator implements OAuth2TokenValidator<Jwt> {
    OAuth2Error error = new OAuth2Error("invalid_token", "The required audience is missing", null);

    public OAuth2TokenValidatorResult validate(Jwt jwt) {
        if (jwt.getAudience().contains("messaging")) {
            return OAuth2TokenValidatorResult.success();
        } else {
            return OAuth2TokenValidatorResult.failure(error);
        }
    }
}

Then, to add into a resource server, it’s a matter of specifying the ReactiveJwtDecoder instance:

@Bean
ReactiveJwtDecoder jwtDecoder() {
    NimbusReactiveJwtDecoder jwtDecoder = (NimbusReactiveJwtDecoder)
            ReactiveJwtDecoders.withOidcIssuerLocation(issuerUri);

    OAuth2TokenValidator<Jwt> audienceValidator = new AudienceValidator();
    OAuth2TokenValidator<Jwt> withIssuer = JwtValidators.createDefaultWithIssuer(issuerUri);
    OAuth2TokenValidator<Jwt> withAudience = new DelegatingOAuth2TokenValidator<>(withIssuer, audienceValidator);

    jwtDecoder.setJwtValidator(withAudience);

    return jwtDecoder;
}