Client Authentication Support

JWT Bearer

Please refer to JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants for further details on JWT Bearer Client Authentication.

The default implementation for JWT Bearer Client Authentication is NimbusJwtClientAuthenticationParametersConverter, which is a Converter that customizes the Token Request parameters by adding a signed JSON Web Token (JWS) in the client_assertion parameter.

The java.security.PrivateKey or javax.crypto.SecretKey used for signing the JWS is supplied by the com.nimbusds.jose.jwk.JWK resolver associated with NimbusJwtClientAuthenticationParametersConverter.

Authenticate using private_key_jwt

Given the following Spring Boot 2.x properties for an OAuth 2.0 Client registration:

spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-authentication-method: private_key_jwt
            authorization-grant-type: authorization_code
            ...

The following example shows how to configure WebClientReactiveAuthorizationCodeTokenResponseClient:

  • Java

  • Kotlin

Function<ClientRegistration, JWK> jwkResolver = (clientRegistration) -> {
	if (clientRegistration.getClientAuthenticationMethod().equals(ClientAuthenticationMethod.PRIVATE_KEY_JWT)) {
		// Assuming RSA key type
		RSAPublicKey publicKey = ...
		RSAPrivateKey privateKey = ...
		return new RSAKey.Builder(publicKey)
				.privateKey(privateKey)
				.keyID(UUID.randomUUID().toString())
				.build();
	}
	return null;
};

WebClientReactiveAuthorizationCodeTokenResponseClient tokenResponseClient =
		new WebClientReactiveAuthorizationCodeTokenResponseClient();
tokenResponseClient.addParametersConverter(
		new NimbusJwtClientAuthenticationParametersConverter<>(jwkResolver));
val jwkResolver: Function<ClientRegistration, JWK> =
    Function<ClientRegistration, JWK> { clientRegistration ->
        if (clientRegistration.clientAuthenticationMethod.equals(ClientAuthenticationMethod.PRIVATE_KEY_JWT)) {
            // Assuming RSA key type
            var publicKey: RSAPublicKey = ...
            var privateKey: RSAPrivateKey = ...
            RSAKey.Builder(publicKey)
                    .privateKey(privateKey)
                    .keyID(UUID.randomUUID().toString())
                .build()
        }
        null
    }

val tokenResponseClient = WebClientReactiveAuthorizationCodeTokenResponseClient()
tokenResponseClient.addParametersConverter(
    NimbusJwtClientAuthenticationParametersConverter(jwkResolver)
)

Authenticate using client_secret_jwt

Given the following Spring Boot 2.x properties for an OAuth 2.0 Client registration:

spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: okta-client-id
            client-secret: okta-client-secret
            client-authentication-method: client_secret_jwt
            authorization-grant-type: client_credentials
            ...

The following example shows how to configure WebClientReactiveClientCredentialsTokenResponseClient:

  • Java

  • Kotlin

Function<ClientRegistration, JWK> jwkResolver = (clientRegistration) -> {
	if (clientRegistration.getClientAuthenticationMethod().equals(ClientAuthenticationMethod.CLIENT_SECRET_JWT)) {
		SecretKeySpec secretKey = new SecretKeySpec(
				clientRegistration.getClientSecret().getBytes(StandardCharsets.UTF_8),
				"HmacSHA256");
		return new OctetSequenceKey.Builder(secretKey)
				.keyID(UUID.randomUUID().toString())
				.build();
	}
	return null;
};

WebClientReactiveClientCredentialsTokenResponseClient tokenResponseClient =
		new WebClientReactiveClientCredentialsTokenResponseClient();
tokenResponseClient.addParametersConverter(
		new NimbusJwtClientAuthenticationParametersConverter<>(jwkResolver));
val jwkResolver = Function<ClientRegistration, JWK?> { clientRegistration: ClientRegistration ->
    if (clientRegistration.clientAuthenticationMethod == ClientAuthenticationMethod.CLIENT_SECRET_JWT) {
        val secretKey = SecretKeySpec(
            clientRegistration.clientSecret.toByteArray(StandardCharsets.UTF_8),
            "HmacSHA256"
        )
        OctetSequenceKey.Builder(secretKey)
            .keyID(UUID.randomUUID().toString())
            .build()
    }
    null
}

val tokenResponseClient = WebClientReactiveClientCredentialsTokenResponseClient()
tokenResponseClient.addParametersConverter(
    NimbusJwtClientAuthenticationParametersConverter(jwkResolver)
)

Customizing the JWT assertion

The JWT produced by NimbusJwtClientAuthenticationParametersConverter contains the iss, sub, aud, jti, iat and exp claims by default. You can customize the headers and/or claims by providing a Consumer<NimbusJwtClientAuthenticationParametersConverter.JwtClientAuthenticationContext<T>> to setJwtClientAssertionCustomizer(). The following example shows how to customize claims of the JWT:

  • Java

  • Kotlin

Function<ClientRegistration, JWK> jwkResolver = ...

NimbusJwtClientAuthenticationParametersConverter<OAuth2ClientCredentialsGrantRequest> converter =
		new NimbusJwtClientAuthenticationParametersConverter<>(jwkResolver);
converter.setJwtClientAssertionCustomizer((context) -> {
	context.getHeaders().header("custom-header", "header-value");
	context.getClaims().claim("custom-claim", "claim-value");
});
val jwkResolver = ...

val converter: NimbusJwtClientAuthenticationParametersConverter<OAuth2ClientCredentialsGrantRequest> =
    NimbusJwtClientAuthenticationParametersConverter(jwkResolver)
converter.setJwtClientAssertionCustomizer { context ->
    context.headers.header("custom-header", "header-value")
    context.claims.claim("custom-claim", "claim-value")
}