CVE-2023-36820: Improper Access Control (CWE-284)
value: Micronaut Security is a security solution for applications. Prior to versions 3.1.2, 3.2.4, 3.3.2, 3.4.3, 3.5.3, 3.6.6, 3.7.4, 3.8.4, 3.9.6, 3.10.2, and 3.11.1, IdTokenClaimsValidator skips `aud` claim validation if token is issued by same identity issuer/provider. Any OIDC setup using Micronaut where multiple OIDC applications exists for the same issuer but token auth are not meant to be shared. This issue has been patched in versions 3.1.2, 3.2.4, 3.3.2, 3.4.3, 3.5.3, 3.6.6, 3.7.4, 3.8.4, 3.9.6, 3.10.2, and 3.11.1.

CWE description: The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
CVSS v3 base score: 6.5
Published: 2023-10-09T14:15Z
Repository: https://github.com/micronaut-projects/micronaut-security
Language: Other
Files changed: security-oauth2/src/main/java/io/micronaut/security/oauth2/client/IdTokenClaimsValidator.java, security-oauth2/src/test/groovy/io/micronaut/security/oauth2/endpoint/token/response/validation/AudienceClaimMatchesClientIdSpec.groovy
Commit date: 2023-06-23 12:36:56 +0200
Commit message: Merge pull request from GHSA-qw22-8w9r-864h

The `aud` claim should contain the Client ID.

https://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation

> Clients MUST validate the ID Token in the Token Response in the following manner:
...
> 1.2. The Issuer Identifier for the OpenID Provider (which is typically obtained during Discovery) MUST exactly match the value of the iss (issuer) Claim.
> 1.3. The Client MUST validate that the aud (audience) Claim contains its client_id value registered at the Issuer identified by the iss (issuer) Claim as an audience.

The audience claim is [validated correctly when obtained from authorisation server.](https://github.com/micronaut-projects/micronaut-security/blob/master/security-oauth2/src/main/java/io/micronaut/security/oauth2/endpoint/token/response/validation/DefaultOpenIdTokenResponseValidator.java#L122) with the [`AudienceClaimValidator`](https://github.com/micronaut-projects/micronaut-security/blob/master/security-oauth2/src/main/java/io/micronaut/security/oauth2/endpoint/token/response/validation/AudienceClaimValidator.java).

However, if the user set `micronaut.security.authentication` to `idtoken`, the token validation of a new request does not validate `aud` claim to match the Client ID if the `iss` claim matched an existing issuer in the application.

This change fixes this vulnerability.
Diff: diff --git a/security-oauth2/src/main/java/io/micronaut/security/oauth2/client/IdTokenClaimsValidator.java b/security-oauth2/src/main/java/io/micronaut/security/oauth2/client/IdTokenClaimsValidator.java
index 2ac54a0d..19caa481 100644
--- a/security-oauth2/src/main/java/io/micronaut/security/oauth2/client/IdTokenClaimsValidator.java
+++ b/security-oauth2/src/main/java/io/micronaut/security/oauth2/client/IdTokenClaimsValidator.java
@@ -197,11 +197,11 @@ public class IdTokenClaimsValidator implements GenericJwtClaimsValidator {
                                                    @NonNull OpenIdClientConfiguration openIdClientConfiguration) {
         if (openIdClientConfiguration.getIssuer().isPresent()) {
             Optional<URL> issuerOptional = openIdClientConfiguration.getIssuer();
             if (issuerOptional.isPresent()) {
                 String issuer = issuerOptional.get().toString();
-                return issuer.equalsIgnoreCase(iss) ||
+                return issuer.equalsIgnoreCase(iss) &&
                         audiences.contains(clientId) &&
                                 validateAzp(claims, clientId, audiences);
             }
         }
         return false;
diff --git a/security-oauth2/src/test/groovy/io/micronaut/security/oauth2/endpoint/token/response/validation/AudienceClaimMatchesClientIdSpec.groovy b/security-oauth2/src/test/groovy/io/micronaut/security/oauth2/endpoint/token/response/validation/AudienceClaimMatchesClientIdSpec.groovy
new file mode 100644
index 00000000..d64474d3
--- /dev/null
+++ b/security-oauth2/src/test/groovy/io/micronaut/security/oauth2/endpoint/token/response/validation/AudienceClaimMatchesClientIdSpec.groovy
@@ -0,0 +1,213 @@
+package io.micronaut.security.oauth2.endpoint.token.response.validation
+
+import com.nimbusds.jose.JWSAlgorithm
+import com.nimbusds.jose.jwk.JWK
+import com.nimbusds.jose.jwk.KeyUse
+import com.nimbusds.jose.jwk.RSAKey
+import com.nimbusds.jose.jwk.gen.JWKGenerator
+import com.nimbusds.jose.jwk.gen.RSAKeyGenerator
+import com.nimbusds.jwt.JWT
+import com.nimbusds.jwt.JWTParser
+import com.nimbusds.jwt.SignedJWT
+import io.micronaut.context.ApplicationContext
+import io.micronaut.context.annotation.Requires
+import io.micronaut.core.util.StringUtils
+import io.micronaut.http.HttpRequest
+import io.micronaut.http.HttpResponse
+import io.micronaut.http.HttpStatus
+import io.micronaut.http.MediaType
+import io.micronaut.http.annotation.Controller
+import io.micronaut.http.annotation.Get
+import io.micronaut.http.annotation.Produces
+import io.micronaut.http.client.BlockingHttpClient
+import io.micronaut.http.client.HttpClient
+import io.micronaut.http.client.exceptions.HttpClientResponseException
+import io.micronaut.http.server.util.HttpHostResolver
+import io.micronaut.runtime.server.EmbeddedServer
+import io.micronaut.security.annotation.Secured
+import io.micronaut.security.authentication.Authentication
+import io.micronaut.security.rules.SecurityRule
+import io.micronaut.security.token.Claims
+import io.micronaut.security.token.generator.TokenGenerator
+import io.micronaut.security.token.jwt.endpoints.JwkProvider
+import io.micronaut.security.token.jwt.generator.AccessTokenConfiguration
+import io.micronaut.security.token.jwt.generator.claims.ClaimsGenerator
+import io.micronaut.security.token.jwt.signature.rsa.RSASignatureGeneratorConfiguration
+import jakarta.inject.Named
+import jakarta.inject.Singleton
+import spock.lang.Specification
+
+import java.security.interfaces.RSAPrivateKey
+import java.security.interfaces.RSAPublicKey
+
+class AudienceClaimMatchesClientIdSpec extends Specification {
+
+    void "test same issuer two different client ids"() {
+        given:
+        EmbeddedServer authServer = ApplicationContext.run(EmbeddedServer, [
+                "micronaut.security.reject-not-found": StringUtils.FALSE,
+                "spec.name": "AudienceClaimMatchesClientIdSpecAuthServer"
+        ])
+        Map<String, Object> configuration = [
+                "micronaut.security.authentication": "idtoken",
+                "micronaut.security.reject-not-found": StringUtils.FALSE,
+                "spec.name": "AudienceClaimMatchesClientIdSpec",
+                "micronaut.security.oauth2.clients.auth.client-id": "AAA",
+                "micronaut.security.oauth2.clients.auth.client-secret": "YYY",
+                'micronaut.security.oauth2.clients.auth.openid.issuer': "http://localhost:${authServer.port}/oauth2/default"]
+        EmbeddedServer server = ApplicationContext.run(EmbeddedServer, configuration)
+        HttpClient authServerHttpClient = server.applicationContext.createBean(HttpClient, authServer.URL)
+        BlockingHttpClient authServerClient = authServerHttpClient.toBlocking()
+
+        when:
+        String keys = authServerClient.retrieve(HttpRequest.GET("/keys"))
+
+        then:
+        noExceptionThrown()
+        keys != '{"keys":[]}'
+
+        when:
+        String clientAToken = authServerClient.retrieve(HttpRequest.GET("/token/clientA").accept(MediaType.TEXT_PLAIN))
+        JWT clientAJWT = JWTParser.parse(clientAToken)
+
+        then:
+        clientAJWT instanceof SignedJWT
+        clientAJWT.getJWTClaimsSet().getClaim("aud") == ["AAA"]
+        clientAJWT.getJWTClaimsSet().getClaim("iss") == "http://localhost:${authServer.port}/oauth2/default"
+
+        when:
+        HttpClient httpClient = server.applicationContext.createBean(HttpClient, server.URL)
+        BlockingHttpClient client = httpClient.toBlocking()
+        client.retrieve(HttpRequest.GET("/hello").bearerAuth(clientAToken))
+
+        then:
+        noExceptionThrown()
+
+        when:
+        String clientBToken = authServerClient.retrieve(HttpRequest.GET("/token/clientB").accept(MediaType.TEXT_PLAIN))
+        JWT clientBJWT = JWTParser.parse(clientBToken)
+
+        then:
+        clientBJWT instanceof SignedJWT
+        clientBJWT.getJWTClaimsSet().getClaim("aud") == ["BBB"]
+        clientBJWT.getJWTClaimsSet().getClaim("iss") == "http://localhost:${authServer.port}/oauth2/default"
+
+        when:
+        client.retrieve(HttpRequest.GET("/hello").bearerAuth(clientBToken))
+
+        then:
+        HttpClientResponseException e = thrown()
+        HttpStatus.UNAUTHORIZED == e.status
+
+        cleanup:
+        authServerClient.close()
+        authServerHttpClient.close()
+        httpClient.close()
+        client.close()
+        server.close()
+        authServer.close()
+    }
+
+    @Requires(property = 'spec.name', value = 'AudienceClaimMatchesClientIdSpec')
+    @Controller("/hello")
+    static class HelloWorldController {
+        @Get
+        @Secured(SecurityRule.IS_AUTHENTICATED)
+        Map<String, String> index() {
+            [message: 'Hello World']
+        }
+    }
+
+    @Requires(property = "spec.name", value="AudienceClaimMatchesClientIdSpecAuthServer")
+    @Secured(SecurityRule.IS_ANONYMOUS)
+    @Controller
+    static class AuthServerController {
+
+        private final HttpHostResolver httpHostResolver
+        private final TokenGenerator tokenGenerator
+        private final AccessTokenConfiguration accessTokenConfiguration
+        private final ClaimsGenerator claimsGenerator
+
+        AuthServerController(HttpHostResolver httpHostResolver,
+                             TokenGenerator tokenGenerator,
+                             AccessTokenConfiguration accessTokenConfiguration,
+                             ClaimsGenerator claimsGenerator) {
+            this.httpHostResolver = httpHostResolver
+            this.tokenGenerator = tokenGenerator
+            this.accessTokenConfiguration = accessTokenConfiguration
+            this.claimsGenerator = claimsGenerator
+        }
+
+        @Produces(MediaType.TEXT_PLAIN)
+        @Get("/token/clientA")
+        HttpResponse<Object> clientA(HttpRequest<?> request) {
+            generateToken(request, "AAA")
+        }
+
+        @Produces(MediaType.TEXT_PLAIN)
+        @Get("/token/clientB")
+        HttpResponse<Object> clientB(HttpRequest<?> request) {
+            generateToken(request, "BBB")
+        }
+
+        private HttpResponse<Object> generateToken(HttpRequest<?> request, String clientId) {
+            String host = httpHostResolver.resolve(request)
+            Map<String, Object> claims = new HashMap<>(claimsGenerator.generateClaims(Authentication.build("sherlock"), accessTokenConfiguration.expiration))
+            claims[Claims.ISSUER] = "${host}/oauth2/default".toString()
+            claims[Claims.AUDIENCE] = clientId
+            tokenGenerator.generateToken(claims).map(HttpResponse::ok).orElseGet(() -> HttpResponse.serverError())
+        }
+
+        @Get("/oauth2/default/.well-known/openid-configuration")
+        String openIdConfiguration(HttpRequest<?> request) {
+            String host = httpHostResolver.resolve(request)
+            '{"issuer":"' + host + '/oauth2/default","authorization_endpoint":"' + host + '/oauth2/default/v1/authorize","token_endpoint":"' + host + '/oauth2/default/v1/token","userinfo_endpoint":"' + host + '/oauth2/default/v1/userinfo","registration_endpoint":"' + host + '/oauth2/v1/clients","jwks_uri":"' + host + '/keys","response_types_supported":["code","id_token","code id_token","code token","id_token token","code id_token token"],"response_modes_supported":["query","fragment","form_post","okta_post_message"],"grant_types_supported":["authorization_code","implicit","refresh_token","password"],"subject_types_supported":["public"],"id_token_signing_alg_values_supported":["RS256"],"scopes_supported":["openid","profile","email","address","phone","offline_access"],"token_endpoint_auth_methods_supported":["client_secret_basic","client_secret_post","client_secret_jwt","private_key_jwt","none"],"claims_supported":["iss","ver","sub","aud","iat","exp","jti","auth_time","amr","idp","nonce","name","nickname","preferred_username","given_name","middle_name","family_name","email","email_verified","profile","zoneinfo","locale","address","phone_number","picture","website","gender","birthdate","updated_at","at_hash","c_hash"],"code_challenge_methods_supported":["S256"],"introspection_endpoint":"' + host + '/oauth2/default/v1/introspect","introspection_endpoint_auth_methods_supported":["client_secret_basic","client_secret_post","client_secret_jwt","private_key_jwt","none"],"revocation_endpoint":"' + host + '/oauth2/default/v1/revoke","revocation_endpoint_auth_methods_supported":["client_secret_basic","client_secret_post","client_secret_jwt","private_key_jwt","none"],"end_session_endpoint":"' + host + '/oauth2/default/v1/logout","request_parameter_supported":true,"request_object_signing_alg_values_supported":["HS256","HS384","HS512","RS256","RS384","RS512","ES256","ES384","ES512"]}'
+        }
+    }
+
+    @Requires(property = 'spec.name', value = 'AudienceClaimMatchesClientIdSpecAuthServer')
+    @Named("generator")
+    @Singleton
+    static class AuthServerSignatureConfiguration implements RSASignatureGeneratorConfiguration, JwkProvider {
+        private final static JWSAlgorithm ALG = JWSAlgorithm.RS256
+        private List<JWK> jwks = null
+        private RSAKey rsaKey = null
+
+        List<JWK> getJwks() {
+            if (jwks == null) {
+                this.jwks = Collections.singletonList(getRsaKey().toPublicJWK())
+            }
+            return jwks
+        }
+
+        RSAKey getRsaKey() {
+            if (rsaKey == null) {
+                JWKGenerator jwkGenerator = new RSAKeyGenerator(2048)
+                        .algorithm(ALG)
+                        .keyUse(KeyUse.SIGNATURE)
+                this.rsaKey = jwkGenerator.generate()
+            }
+            return rsaKey
+        }
+
+        @Override
+        RSAPublicKey getPublicKey() {
+            getRsaKey().toRSAPublicKey()
+        }
+
+        @Override
+        RSAPrivateKey getPrivateKey() {
+            getRsaKey().toRSAPrivateKey()
+        }
+
+        @Override
+        JWSAlgorithm getJwsAlgorithm() {
+            ALG
+        }
+
+        @Override
+        List<JWK> retrieveJsonWebKeys() {
+            getJwks()
+        }
+    }
+}

Vulnerable code:                 return issuer.equalsIgnoreCase(iss) ||
Fixed code:                 return issuer.equalsIgnoreCase(iss) &&
package io.micronaut.security.oauth2.endpoint.token.response.validation

import com.nimbusds.jose.JWSAlgorithm
import com.nimbusds.jose.jwk.JWK
import com.nimbusds.jose.jwk.KeyUse
import com.nimbusds.jose.jwk.RSAKey
import com.nimbusds.jose.jwk.gen.JWKGenerator
import com.nimbusds.jose.jwk.gen.RSAKeyGenerator
import com.nimbusds.jwt.JWT
import com.nimbusds.jwt.JWTParser
import com.nimbusds.jwt.SignedJWT
import io.micronaut.context.ApplicationContext
import io.micronaut.context.annotation.Requires
import io.micronaut.core.util.StringUtils
import io.micronaut.http.HttpRequest
import io.micronaut.http.HttpResponse
import io.micronaut.http.HttpStatus
import io.micronaut.http.MediaType
import io.micronaut.http.annotation.Controller
import io.micronaut.http.annotation.Get
import io.micronaut.http.annotation.Produces
import io.micronaut.http.client.BlockingHttpClient
import io.micronaut.http.client.HttpClient
import io.micronaut.http.client.exceptions.HttpClientResponseException
import io.micronaut.http.server.util.HttpHostResolver
import io.micronaut.runtime.server.EmbeddedServer
import io.micronaut.security.annotation.Secured
import io.micronaut.security.authentication.Authentication
import io.micronaut.security.rules.SecurityRule
import io.micronaut.security.token.Claims
import io.micronaut.security.token.generator.TokenGenerator
import io.micronaut.security.token.jwt.endpoints.JwkProvider
import io.micronaut.security.token.jwt.generator.AccessTokenConfiguration
import io.micronaut.security.token.jwt.generator.claims.ClaimsGenerator
import io.micronaut.security.token.jwt.signature.rsa.RSASignatureGeneratorConfiguration
import jakarta.inject.Named
import jakarta.inject.Singleton
import spock.lang.Specification

import java.security.interfaces.RSAPrivateKey
import java.security.interfaces.RSAPublicKey

class AudienceClaimMatchesClientIdSpec extends Specification {

    void "test same issuer two different client ids"() {
        given:
        EmbeddedServer authServer = ApplicationContext.run(EmbeddedServer, [
                "micronaut.security.reject-not-found": StringUtils.FALSE,
                "spec.name": "AudienceClaimMatchesClientIdSpecAuthServer"
        ])
        Map<String, Object> configuration = [
                "micronaut.security.authentication": "idtoken",
                "micronaut.security.reject-not-found": StringUtils.FALSE,
                "spec.name": "AudienceClaimMatchesClientIdSpec",
                "micronaut.security.oauth2.clients.auth.client-id": "AAA",
                "micronaut.security.oauth2.clients.auth.client-secret": "YYY",
                'micronaut.security.oauth2.clients.auth.openid.issuer': "http://localhost:${authServer.port}/oauth2/default"]
        EmbeddedServer server = ApplicationContext.run(EmbeddedServer, configuration)
        HttpClient authServerHttpClient = server.applicationContext.createBean(HttpClient, authServer.URL)
        BlockingHttpClient authServerClient = authServerHttpClient.toBlocking()

        when:
        String keys = authServerClient.retrieve(HttpRequest.GET("/keys"))

        then:
        noExceptionThrown()
        keys != '{"keys":[]}'

        when:
        String clientAToken = authServerClient.retrieve(HttpRequest.GET("/token/clientA").accept(MediaType.TEXT_PLAIN))
        JWT clientAJWT = JWTParser.parse(clientAToken)

        then:
        clientAJWT instanceof SignedJWT
        clientAJWT.getJWTClaimsSet().getClaim("aud") == ["AAA"]
        clientAJWT.getJWTClaimsSet().getClaim("iss") == "http://localhost:${authServer.port}/oauth2/default"

        when:
        HttpClient httpClient = server.applicationContext.createBean(HttpClient, server.URL)
        BlockingHttpClient client = httpClient.toBlocking()
        client.retrieve(HttpRequest.GET("/hello").bearerAuth(clientAToken))

        then:
        noExceptionThrown()

        when:
        String clientBToken = authServerClient.retrieve(HttpRequest.GET("/token/clientB").accept(MediaType.TEXT_PLAIN))
        JWT clientBJWT = JWTParser.parse(clientBToken)

        then:
        clientBJWT instanceof SignedJWT
        clientBJWT.getJWTClaimsSet().getClaim("aud") == ["BBB"]
        clientBJWT.getJWTClaimsSet().getClaim("iss") == "http://localhost:${authServer.port}/oauth2/default"

        when:
        client.retrieve(HttpRequest.GET("/hello").bearerAuth(clientBToken))

        then:
        HttpClientResponseException e = thrown()
        HttpStatus.UNAUTHORIZED == e.status

        cleanup:
        authServerClient.close()
        authServerHttpClient.close()
        httpClient.close()
        client.close()
        server.close()
        authServer.close()
    }

    @Requires(property = 'spec.name', value = 'AudienceClaimMatchesClientIdSpec')
    @Controller("/hello")
    static class HelloWorldController {
        @Get
        @Secured(SecurityRule.IS_AUTHENTICATED)
        Map<String, String> index() {
            [message: 'Hello World']
        }
    }

    @Requires(property = "spec.name", value="AudienceClaimMatchesClientIdSpecAuthServer")
    @Secured(SecurityRule.IS_ANONYMOUS)
    @Controller
    static class AuthServerController {

        private final HttpHostResolver httpHostResolver
        private final TokenGenerator tokenGenerator
        private final AccessTokenConfiguration accessTokenConfiguration
        private final ClaimsGenerator claimsGenerator

        AuthServerController(HttpHostResolver httpHostResolver,
                             TokenGenerator tokenGenerator,
                             AccessTokenConfiguration accessTokenConfiguration,
                             ClaimsGenerator claimsGenerator) {
            this.httpHostResolver = httpHostResolver
            this.tokenGenerator = tokenGenerator
            this.accessTokenConfiguration = accessTokenConfiguration
            this.claimsGenerator = claimsGenerator
        }

        @Produces(MediaType.TEXT_PLAIN)
        @Get("/token/clientA")
        HttpResponse<Object> clientA(HttpRequest<?> request) {
            generateToken(request, "AAA")
        }

        @Produces(MediaType.TEXT_PLAIN)
        @Get("/token/clientB")
        HttpResponse<Object> clientB(HttpRequest<?> request) {
            generateToken(request, "BBB")
        }

        private HttpResponse<Object> generateToken(HttpRequest<?> request, String clientId) {
            String host = httpHostResolver.resolve(request)
            Map<String, Object> claims = new HashMap<>(claimsGenerator.generateClaims(Authentication.build("sherlock"), accessTokenConfiguration.expiration))
            claims[Claims.ISSUER] = "${host}/oauth2/default".toString()
            claims[Claims.AUDIENCE] = clientId
            tokenGenerator.generateToken(claims).map(HttpResponse::ok).orElseGet(() -> HttpResponse.serverError())
        }

        @Get("/oauth2/default/.well-known/openid-configuration")
        String openIdConfiguration(HttpRequest<?> request) {
            String host = httpHostResolver.resolve(request)
            '{"issuer":"' + host + '/oauth2/default","authorization_endpoint":"' + host + '/oauth2/default/v1/authorize","token_endpoint":"' + host + '/oauth2/default/v1/token","userinfo_endpoint":"' + host + '/oauth2/default/v1/userinfo","registration_endpoint":"' + host + '/oauth2/v1/clients","jwks_uri":"' + host + '/keys","response_types_supported":["code","id_token","code id_token","code token","id_token token","code id_token token"],"response_modes_supported":["query","fragment","form_post","okta_post_message"],"grant_types_supported":["authorization_code","implicit","refresh_token","password"],"subject_types_supported":["public"],"id_token_signing_alg_values_supported":["RS256"],"scopes_supported":["openid","profile","email","address","phone","offline_access"],"token_endpoint_auth_methods_supported":["client_secret_basic","client_secret_post","client_secret_jwt","private_key_jwt","none"],"claims_supported":["iss","ver","sub","aud","iat","exp","jti","auth_time","amr","idp","nonce","name","nickname","preferred_username","given_name","middle_name","family_name","email","email_verified","profile","zoneinfo","locale","address","phone_number","picture","website","gender","birthdate","updated_at","at_hash","c_hash"],"code_challenge_methods_supported":["S256"],"introspection_endpoint":"' + host + '/oauth2/default/v1/introspect","introspection_endpoint_auth_methods_supported":["client_secret_basic","client_secret_post","client_secret_jwt","private_key_jwt","none"],"revocation_endpoint":"' + host + '/oauth2/default/v1/revoke","revocation_endpoint_auth_methods_supported":["client_secret_basic","client_secret_post","client_secret_jwt","private_key_jwt","none"],"end_session_endpoint":"' + host + '/oauth2/default/v1/logout","request_parameter_supported":true,"request_object_signing_alg_values_supported":["HS256","HS384","HS512","RS256","RS384","RS512","ES256","ES384","ES512"]}'
        }
    }

    @Requires(property = 'spec.name', value = 'AudienceClaimMatchesClientIdSpecAuthServer')
    @Named("generator")
    @Singleton
    static class AuthServerSignatureConfiguration implements RSASignatureGeneratorConfiguration, JwkProvider {
        private final static JWSAlgorithm ALG = JWSAlgorithm.RS256
        private List<JWK> jwks = null
        private RSAKey rsaKey = null

        List<JWK> getJwks() {
            if (jwks == null) {
                this.jwks = Collections.singletonList(getRsaKey().toPublicJWK())
            }
            return jwks
        }

        RSAKey getRsaKey() {
            if (rsaKey == null) {
                JWKGenerator jwkGenerator = new RSAKeyGenerator(2048)
                        .algorithm(ALG)
                        .keyUse(KeyUse.SIGNATURE)
                this.rsaKey = jwkGenerator.generate()
            }
            return rsaKey
        }

        @Override
        RSAPublicKey getPublicKey() {
            getRsaKey().toRSAPublicKey()
        }

        @Override
        RSAPrivateKey getPrivateKey() {
            getRsaKey().toRSAPrivateKey()
        }

        @Override
        JWSAlgorithm getJwsAlgorithm() {
            ALG
        }

        @Override
        List<JWK> retrieveJsonWebKeys() {
            getJwks()
        }
    }
}