How do I change the default signing algorithm in Spring OAuth2?

Question

I need implement in my application JWT authentication. So I made this code by OAuth2 guide on spring site. It is working nicely, but by default is using the SHA256 signing algorithm.

Can you tell me how to change my code to use SHA512 or some other algorithm?

Here is my implementation:

@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    @Value("${security.signing-key}")
    private String signingKey;

    @Value("${security.encoding-strength}")
    private Integer encodingStrength;

    @Value("${security.security-realm}")
    private String securityRealm;

    @Autowired
    private UserDetailsService userDetailsService;

    @Bean
    @Override
    protected AuthenticationManager authenticationManager() throws Exception {
        return super.authenticationManager();
    }

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth.userDetailsService(userDetailsService)
                .passwordEncoder(new BCryptPasswordEncoder());
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
                .sessionManagement()
                .sessionCreationPolicy(SessionCreationPolicy.STATELESS)
                .and()
                .httpBasic()
                .realmName(securityRealm)
                .and()
                .csrf()
                .disable();

    }

    @Bean
    public JwtAccessTokenConverter accessTokenConverter() {
        JwtAccessTokenConverter converter = new JwtAccessTokenConverter();
        converter.setSigningKey(signingKey);
        return converter;
    }

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

    @Bean
    @Primary
    //Making this primary to avoid any accidental duplication with another token service instance of the same name
    public DefaultTokenServices tokenServices() {
        DefaultTokenServices defaultTokenServices = new DefaultTokenServices();
        defaultTokenServices.setTokenStore(tokenStore());
        defaultTokenServices.setSupportRefreshToken(true);
        return defaultTokenServices;
    }
}

Authorization Server:

@Configuration
@EnableAuthorizationServer
public class AuthorizationServerConfig extends AuthorizationServerConfigurerAdapter {
    @Value("${security.jwt.client-id}")
    private String clientId;

    @Value("${security.jwt.client-secret}")
    private String clientSecret;

    @Value("${security.jwt.grant-type}")
    private String grantType;

    @Value("${security.jwt.scope-read}")
    private String scopeRead;

    @Value("${security.jwt.scope-write}")
    private String scopeWrite = "write";

    @Value("${security.jwt.resource-ids}")
    private String resourceIds;

    @Value("${security.jwt.expiration}")
    private int expiration;

    @Autowired
    private TokenStore tokenStore;

    @Autowired
    private JwtAccessTokenConverter accessTokenConverter;

    @Autowired
    private AuthenticationManager authenticationManager;

    @Override
    public void configure(ClientDetailsServiceConfigurer configurer) throws Exception {
        configurer
                .inMemory()
                .withClient(clientId)
                .secret(clientSecret)
                .authorizedGrantTypes(grantType)
                .scopes(scopeRead, scopeWrite)
                .resourceIds(resourceIds)
                .accessTokenValiditySeconds(expiration);
    }

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {
        TokenEnhancerChain enhancerChain = new TokenEnhancerChain();
        enhancerChain.setTokenEnhancers(Arrays.asList(accessTokenConverter));
        endpoints.tokenStore(tokenStore)
                .accessTokenConverter(accessTokenConverter)
                .tokenEnhancer(enhancerChain)
                .authenticationManager(authenticationManager);
    }
}

Resource server:

@Configuration
@EnableResourceServer
public class ResourceServerConfig extends ResourceServerConfigurerAdapter {
    @Autowired
    private ResourceServerTokenServices tokenServices;

    @Value("${security.jwt.resource-ids}")
    private String resourceIds;

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

    @Override
    public void configure(HttpSecurity http) throws Exception {
        http
                .requestMatchers()
                .and()
                .authorizeRequests()
                .antMatchers("/actuator/**", "/api-docs/**").permitAll()
                .antMatchers("/springjwt/**" ).authenticated();
    }
}

Answer 1

Since version 2.0.12 of Spring Security OAuth2 you can set the signer, see Unable to configure the algorithm used for signing and verifying:

desmondrawls commented on 7 Oct 2016

We need the RsaSigner and RsaVerifier classes to use sha512 instead of sha256. Because the JwtAccessTokenConverter instantiates these classes with their default algorithm, sha256, it seems like the only way to configure the algorithm would be to extend the JwtAccessTokenConverter, RsaSigner, and RsaVerifier while rewriting the package-protected RsaKeyHelper. We don't want to maintain that many spring-security classes. How else could we do this? Could the JwtAccessTokenConverter be rewritten to allow easier configuration of the algorithm?

and JwtAccessTokenConverter:

public void setVerifier(org.springframework.security.jwt.crypto.sign.SignatureVerifier verifier)

Unconditionally set the verifier (the verifer key is then ignored).

[...]

public void setSigner(org.springframework.security.jwt.crypto.sign.Signer signer)

Unconditionally set the signer to use (if needed). The signer key is then ignored.