我遇到了同样的问题，访问令牌响应和请求不符合oAuth2标准。下面是我的代码（它在Kotlin中，但对于java开发人员来说也应该是可以理解的），用于spring Boot 版本2.3.6.RELEASE。Gradle依赖项：

implementation(enforcedPlatform("org.springframework.boot:spring-boot-dependencies:${springBootVersion}"))
implementation("org.springframework.boot:spring-boot-starter-webflux")
implementation("org.springframework.boot:spring-boot-starter-oauth2-client")

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在添加它们之后，你必须首先创建你的自定义令牌请求/响应客户端，它将实现ReactiveOAuth2AccessTokenResponseClient接口：

class CustomTokenResponseClient : ReactiveOAuth2AccessTokenResponseClient<OAuth2ClientCredentialsGrantRequest> {
    private val webClient = WebClient.builder().build()
    override fun getTokenResponse(
            authorizationGrantRequest: OAuth2ClientCredentialsGrantRequest
    ): Mono<OAuth2AccessTokenResponse> =
            webClient.post()
                    .uri(authorizationGrantRequest.clientRegistration.providerDetails.tokenUri)
                    .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
                    .bodyValue(CustomTokenRequest(
                            clientId = authorizationGrantRequest.clientRegistration.clientId,
                            clientSecret = authorizationGrantRequest.clientRegistration.clientSecret
                    ))
                    .exchange()
                    .flatMap { it.bodyToMono<NotStandardTokenResponse>() }
                    .map { it.toOAuth2AccessTokenResponse() }
    private fun NotStandardTokenResponse.toOAuth2AccessTokenResponse() = OAuth2AccessTokenResponse
            .withToken(this.accessToken)
            .refreshToken(this.refreshToken)
            .expiresIn(convertExpirationDateToDuration(this.data.expires).toSeconds())
            .tokenType(OAuth2AccessToken.TokenType.BEARER)
            .build()
}

型
正如您在上面看到的，在这个类中，您可以根据您的特定需求调整令牌请求/响应处理。
注意事项：getTokenResponse方法中的authorizationGrantRequest参数。Spring在这里传递来自应用程序属性的数据，因此在定义它们时遵循标准，例如，它们可能看起来像这样：

spring:
  security:
    oauth2:
      client:
        registration:
          name-for-oauth-integration:
            authorization-grant-type: client_credentials
            client-id: id
            client-secret: secret
        provider:
          name-for-oauth-integration:
            token-uri: https://oauth.com/token

型
最后一步是在oAuth2配置中使用CustomTokenResponseClient，它可能看起来像这样：

@Configuration
class CustomOAuth2Configuration {
    @Bean
    fun customOAuth2WebWebClient(clientRegistrations: ReactiveClientRegistrationRepository): WebClient {
        val clientRegistryRepo = InMemoryReactiveClientRegistrationRepository(
                clientRegistrations.findByRegistrationId("name-for-oauth-integration").block()
        )
        val clientService = InMemoryReactiveOAuth2AuthorizedClientService(clientRegistryRepo)
        val authorizedClientManager =
                AuthorizedClientServiceReactiveOAuth2AuthorizedClientManager(clientRegistryRepo, clientService)
        val authorizedClientProvider = ClientCredentialsReactiveOAuth2AuthorizedClientProvider()
        authorizedClientProvider.setAccessTokenResponseClient(CustomTokenResponseClient())
        authorizedClientManager.setAuthorizedClientProvider(authorizedClientProvider)
        val oauthFilter = ServerOAuth2AuthorizedClientExchangeFilterFunction(authorizedClientManager)
        oauthFilter.setDefaultClientRegistrationId("name-for-oauth-integration")
        return WebClient.builder()
                .filter(oauthFilter)
                .build()
    }
}

型

现在，这是可能的，但不是优雅的。
请注意，您可以为ServerOAuth2AuthorizedClientExchangeFilterFunction提供自定义的ReactiveOAuth2AccessTokenResponseClient。
您可以通过复制WebClientReactiveClientCredentialsTokenResponseClient的内容来创建自己的实现，从而添加所需的任何其他参数。
也就是说，如果有一个setter来使其更方便，那就更好了。

下面是我在进一步调查后发现的。我的问题中描述的代码永远不会调用client_credentials并适合我的用例。我认为（不是100%确定）如果我试图在微服务架构中的多个服务中传播用户提交的令牌，它将在未来非常有用。像这样的动作链浮现在脑海中：
用户调用服务A ->服务A调用服务B ->服务B响应->服务A响应用户请求。
并使用相同的令牌开始与通过整个过程。

我的用例解决方案：

我所做的是在很大程度上基于原始类创建一个新的Filter类，并在执行请求之前执行一个步骤，检查是否存储了可用于Auth 0 Management API的JWT令牌。如果没有，我构建client_credentials grant请求并获取一个，然后把这个token作为一个bearer附加到初始请求上，然后执行那个请求。我还在-内存缓存机制，以便如果令牌有效，以后的任何其他请求都将使用它。

过滤器

public class Auth0ClientCredentialsGrantFilterFunction implements ExchangeFilterFunction {
    private ReactiveClientRegistrationRepository clientRegistrationRepository;
    /**
     * Required by auth0 when requesting a client credentials token
     */
    private String audience;
    private String clientRegistrationId;
    private Auth0InMemoryAccessTokenStore auth0InMemoryAccessTokenStore;
    public Auth0ClientCredentialsGrantFilterFunction(ReactiveClientRegistrationRepository clientRegistrationRepository,
                                                     String clientRegistrationId,
                                                     String audience) {
        this.clientRegistrationRepository = clientRegistrationRepository;
        this.audience = audience;
        this.clientRegistrationId = clientRegistrationId;
        this.auth0InMemoryAccessTokenStore = new Auth0InMemoryAccessTokenStore();
    }
    public void setAuth0InMemoryAccessTokenStore(Auth0InMemoryAccessTokenStore auth0InMemoryAccessTokenStore) {
        this.auth0InMemoryAccessTokenStore = auth0InMemoryAccessTokenStore;
    }
    @Override
    public Mono<ClientResponse> filter(ClientRequest request, ExchangeFunction next) {
        return auth0ClientCredentialsToken(next)
                .map(token -> bearer(request, token.getTokenValue()))
                .flatMap(next::exchange)
                .switchIfEmpty(next.exchange(request));
    }
    private Mono<OAuth2AccessToken> auth0ClientCredentialsToken(ExchangeFunction next) {
        return Mono.defer(this::loadClientRegistration)
                .map(clientRegistration -> new ClientCredentialsRequest(clientRegistration, audience))
                .flatMap(request -> this.auth0InMemoryAccessTokenStore.retrieveToken()
                        .switchIfEmpty(refreshAuth0Token(request, next)));
    }
    private Mono<OAuth2AccessToken> refreshAuth0Token(ClientCredentialsRequest clientCredentialsRequest, ExchangeFunction next) {
        ClientRegistration clientRegistration = clientCredentialsRequest.getClientRegistration();
        String tokenUri = clientRegistration
                .getProviderDetails().getTokenUri();
        ClientRequest clientCredentialsTokenRequest = ClientRequest.create(HttpMethod.POST, URI.create(tokenUri))
                .header(HttpHeaders.ACCEPT, MediaType.APPLICATION_JSON_VALUE)
                .body(clientCredentialsTokenBody(clientCredentialsRequest))
                .build();
        return next.exchange(clientCredentialsTokenRequest)
                .flatMap(response -> response.body(oauth2AccessTokenResponse()))
                .map(OAuth2AccessTokenResponse::getAccessToken)
                .doOnNext(token -> this.auth0InMemoryAccessTokenStore.storeToken(token));
    }
    private static BodyInserters.FormInserter<String> clientCredentialsTokenBody(ClientCredentialsRequest clientCredentialsRequest) {
        ClientRegistration clientRegistration = clientCredentialsRequest.getClientRegistration();
        return BodyInserters
                .fromFormData("grant_type", AuthorizationGrantType.CLIENT_CREDENTIALS.getValue())
                .with("client_id", clientRegistration.getClientId())
                .with("client_secret", clientRegistration.getClientSecret())
                .with("audience", clientCredentialsRequest.getAudience());
    }
    private Mono<ClientRegistration> loadClientRegistration() {
        return Mono.just(clientRegistrationId)
                .flatMap(r -> clientRegistrationRepository.findByRegistrationId(r));
    }
    private ClientRequest bearer(ClientRequest request, String token) {
        return ClientRequest.from(request)
                .headers(headers -> headers.setBearerAuth(token))
                .build();
    }
    static class ClientCredentialsRequest {
        private final ClientRegistration clientRegistration;
        private final String audience;
        public ClientCredentialsRequest(ClientRegistration clientRegistration, String audience) {
            this.clientRegistration = clientRegistration;
            this.audience = audience;
        }
        public ClientRegistration getClientRegistration() {
            return clientRegistration;
        }
        public String getAudience() {
            return audience;
        }
    }
}

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代币存储

public class Auth0InMemoryAccessTokenStore implements ReactiveInMemoryAccessTokenStore {
    private AtomicReference<OAuth2AccessToken> token = new AtomicReference<>();
    private Clock clock = Clock.systemUTC();
    private Duration accessTokenExpiresSkew = Duration.ofMinutes(1);
    public Auth0InMemoryAccessTokenStore() {
    }
    @Override
    public Mono<OAuth2AccessToken> retrieveToken() {
        return Mono.justOrEmpty(token.get())
                .filter(Objects::nonNull)
                .filter(token -> token.getExpiresAt() != null)
                .filter(token -> {
                    Instant now = this.clock.instant();
                    Instant expiresAt = token.getExpiresAt();
                    if (now.isBefore(expiresAt.minus(this.accessTokenExpiresSkew))) {
                        return true;
                    }
                    return false;
                });
    }
    @Override
    public Mono<Void> storeToken(OAuth2AccessToken token) {
        this.token.set(token);
        return Mono.empty();
    }
}

型

令牌存储接口

public interface ReactiveInMemoryAccessTokenStore {
    Mono<OAuth2AccessToken> retrieveToken();
    Mono<Void> storeToken(OAuth2AccessToken token);
}

型
最后定义并使用这些bean。

@Bean
    public Auth0ClientCredentialsGrantFilterFunction auth0FilterFunction(ReactiveClientRegistrationRepository clientRegistrations,
                                                                         @Value("${auth0.client-registration-id}") String clientRegistrationId,
                                                                         @Value("${auth0.audience}") String audience) {
        return new Auth0ClientCredentialsGrantFilterFunction(clientRegistrations, clientRegistrationId, audience);
    }
    @Bean(name = "auth0-webclient")
    WebClient webClient(Auth0ClientCredentialsGrantFilterFunction filter) {
        return WebClient.builder()
                .filter(filter)
                .build();
    }

型
此时令牌存储有一个小问题，因为client_credentials令牌请求将在同时到来的并行请求上执行多个，但我可以在可预见的未来接受这一点。

您的application.yml缺少一个变量：client-authentication-method：post
应该是这样的：

spring:
 security:
  oauth2:
   client:
    provider:
     auth0-client:
      token-uri: https://XXXX.auth0.com//
    registration:
     auth0-client:
      client-id: Client
      client-secret: Secret
      authorization_grant_type: client_credentials
      client-authentication-method: post

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如果没有它，我总是得到“invalid_client”的响应。
在Spring罩2.7.2中进行测试

还有另一种方法可以解决这个问题。如果对auth0.com API的client_credentials令牌请求在请求主体中不包括audience字段，那么auth0.com将默认为https://jwtresourceapi。因此，为了能够使用WebClient，上面@DArkO提供的（令人惊叹的）解决方案，您可以在https://jwtresourceapi的受众中使用auth0.com创建所有API。
我不知道你还需要什么，但我所做的只是在auth0.com中定义一个API，我可以有多个应用程序。只要应用程序在API的机器对机器应用程序中被授权，它就可以工作。
请记住，auth0.com只是一个开发者的Playground，我不会用它来创建生产就绪的应用程序。
PS>我还必须在配置文件中包含authorization-grant-type: client_credentials，尽管配置bean示例说我不需要它。也许我稍后会弄清楚，但现在这是有效的。