How to configure spring authorization to sign jwt tokens using existing jwks keys

Question

Good Day,

My situations is as follows. I have one resource server and two authorization servers.

The first authorization server(Not maintained by us) uses a set of jwks to sign jwt token whenever someone logs in via their portal. Our resource server is already configured to verify the signature of the tokens using "JwkTokenStore(url path to jwks)".

I now want to configure our authorization server to sign jwt tokens using the same jwks set when someone logs in via our portal.

The idea being that if the tokens are signed in the same way, the resource server should be able to verify the signature regardless of which auth server issued the tokens.

Is this a feesable solution to the question of having two auth servers and one resource server ?

Below is snippets of how the resource server is configured.

Resource Server Config

@Configuration
@EnableResourceServer
@Order(3)
@Slf4j
public class ResourceServerConfiguration extends ResourceServerConfigurerAdapter {

    @Value("${spring.security.oauth2.resourceserver.jwt.jwk-set-uri}")
    private String keys;
    @Autowired
    private CustomAccessTokenConverter customAccessTokenConverter;

    @Override
    public void configure(HttpSecurity http) throws Exception {

        http.authorizeRequests().authenticated().and().oauth2ResourceServer().jwt();
    }

    @Override
    public void configure(ResourceServerSecurityConfigurer config) {
        config.tokenServices(tokenServices());
        config.resourceId(null);
    }

    @Bean TokenStore tokenStore() throws IOException {
        JwkTokenStore store = new JwkTokenStore(keys);
        return store;
    }

    @Bean
    public JwtAccessTokenConverter accessTokenConverter() {
        JwtAccessTokenConverter converter = new JwtAccessTokenConverter();
        converter.setAccessTokenConverter(customAccessTokenConverter);
        return converter;
    }


    @Bean
    public DefaultTokenServices tokenServices() {
        DefaultTokenServices defaultTokenServices = new DefaultTokenServices();
        try {
            defaultTokenServices.setTokenStore(tokenStore());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return defaultTokenServices;
    }
}  

CustomAccessTokenConverter

@Component
public class CustomAccessTokenConverter extends DefaultAccessTokenConverter {

    @Override
    public OAuth2Authentication extractAuthentication(Map<String, ?> claims) {
        OAuth2Authentication authentication = super.extractAuthentication(claims);
        authentication.setDetails(claims);
        return authentication;
    }
}  

Application Properties

spring.security.oauth2.resourceserver.jwt.jwk-set-uri=https://auth.server.one/keys.json

So how do I go about configuring our own auth server so that it signs jwt tokens using the same jwks set of keys. I have the following so far but the error I get is when trying to login with password grant.

"Handling error: JwkException, This operation is not supported."

@Configuration
@EnableAuthorizationServer
public class AuthServerConfig extends AuthorizationServerConfigurerAdapter {

    @Override
    public void configure(ClientDetailsServiceConfigurer clients) throws  Exception {
        clients.inMemory()
            .withClient(clientId)
            .secret(passwordEncoder.encode(clientSecret))
            .scopes("read")
            .accessTokenValiditySeconds(300)
            .refreshTokenValiditySeconds(86400)
            .authorizedGrantTypes("client_credentials", "password", "refresh_token");
    }

    @Bean
    public TokenStore tokenStore() {
        JwkTokenStore store = new JwkTokenStore("https://auth.server.one/keys.json");
        return store;
    }

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

Any help will be greatly appreciated. Thanks All