如何在Ballerina客户端凭证授权类型中添加额外认证参数？

需要发送的OAuth2 token请求如下：

curl --request POST --url https://dev-jlsubxnitkpok2tw.au.auth0.com/oauth/token 
--header 'content-type: application/json' \
--data '{"client_id":"","client_secret":"","audience":"","grant_type":"client_credentials"}'

当前使用的Ballerina客户端代码：

http:Client securedEP = check new ("http://postman-echo.com", {
            auth: {
                tokenUrl: "xxx/oauth/token",
                clientId: "xxx",
                clientSecret: "xxx",
                scopes: ["read", "submit"]
            }
        });

服务返回错误：

cause: Failed to get a success response from the endpoint. Response code: '403'. 
Response body: '{"error":"access_denied","error_description":"No audience 
parameter was provided, and no default audience has been configured"}'

在Ballerina的http:Client配置的auth对象中，直接添加audience字段即可，该字段对应OAuth2 Client Credentials模式请求中需要的audience参数。修改后的代码如下：

http:Client securedEP = check new ("http://postman-echo.com", {
            auth: {
                tokenUrl: "xxx/oauth/token",
                clientId: "xxx",
                clientSecret: "xxx",
                scopes: ["read", "submit"],
                audience: "your-audience-value" // 替换为实际的audience值
            }
        });

当使用Client Credentials授权类型时，Ballerina的HTTP客户端会自动构造包含audience参数的token请求，匹配你提供的curl请求格式，从而解决服务返回的403错误。

内容的提问来源于stack exchange，提问作者Rukshan Perera