Client Authentication Support

Client Credentials

Authenticate using client_secret_basic

Client Authentication with HTTP Basic is supported out of the box and no customization is necessary to enable it. The default implementation is provided by DefaultOAuth2TokenRequestHeadersConverter.

Given the following Spring Boot properties for an OAuth 2.0 client registration:

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

The following example shows how to configure WebClientReactiveAuthorizationCodeTokenResponseClient to disable URL encoding of the client credentials:

  • Java

  • Kotlin

DefaultOAuth2TokenRequestHeadersConverter<OAuth2AuthorizationCodeGrantRequest> headersConverter =
		new DefaultOAuth2TokenRequestHeadersConverter<>();
headersConverter.setEncodeClientCredentials(false);

WebClientReactiveAuthorizationCodeTokenResponseClient tokenResponseClient =
		new WebClientReactiveAuthorizationCodeTokenResponseClient();
tokenResponseClient.setHeadersConverter(headersConverter);
val headersConverter = DefaultOAuth2TokenRequestHeadersConverter<OAuth2AuthorizationCodeGrantRequest>()
headersConverter.setEncodeClientCredentials(false)

val tokenResponseClient = WebClientReactiveAuthorizationCodeTokenResponseClient()
tokenResponseClient.setHeadersConverter(headersConverter)

Authenticate using client_secret_post

Client Authentication with client credentials included in the request-body is supported out of the box and no customization is necessary to enable it.

The following Spring Boot properties for an OAuth 2.0 client registration demonstrate the configuration:

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

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 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 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")
}

Public Authentication

Public Client Authentication is supported out of the box and no customization is necessary to enable it.

The following Spring Boot properties for an OAuth 2.0 client registration demonstrate the configuration:

spring:
  security:
    oauth2:
      client:
        registration:
          okta:
            client-id: client-id
            client-authentication-method: none
            authorization-grant-type: authorization_code
            ...
Public Clients are supported using Proof Key for Code Exchange (PKCE). PKCE will automatically be used when client-authentication-method is set to "none" (ClientAuthenticationMethod.NONE).