我想通过其客户端凭证直接访问一个 API，而不是通过任何 Web 应用程序private async Task<string> GetAutheticationToken(string APITypeSelected, string APIKeySelected=null)    {        string aadInstance = ConfigurationManager.AppSettings["ida:AADInstance"];        string tenant = ConfigurationManager.AppSettings["ida:AADTenant"];        string appKey = ConfigurationManager.AppSettings[APIKeySelected];        string apiID = ConfigurationManager.AppSettings[APITypeSelected];        //appKey = HttpUtility.UrlEncode(appKey);        string authority = String.Format(CultureInfo.InvariantCulture, aadInstance, tenant);        using (HttpClient client = new HttpClient())        {            Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext authContext = null;            ClientCredential clientCredential = null;            authContext = new Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext(authority);            //encodeURIComponent(client_secret);            clientCredential = new ClientCredential(apiID, appKey);            AuthenticationResult authResult = null;            authResult = await authContext.AcquireTokenAsync(apiID, clientCredential);            return authResult.AccessToken;        }    }执行时我在这一行收到以下错误（AADSTS501051）authResult = await authContext.AcquireTokenAsync(apiID, clientCredential);AADSTS501051：应用程序“{API GUID}”(DEV-API) 未分配给应用程序“{API GUID}”(DEV-API) 的角色。我是否必须向其自身授予 API 权限？我需要做什么。