如何修复调用 GetAccessTokenForAppAsync 以获取导致 NullReferenceException 的令牌？

Question

我正在研究如何在 ASP.NET Core 3.1 Razor Pages 应用程序中使用 Microsoft Graph API。我找到了 this 指南并使其大部分工作（以及检索令牌），直到我意识到我需要在没有用户的情况下访问 API。

目前，我卡住了，因为我无法使用 ITokenAcquisition GetAccessTokenForAppAsync 方法检索令牌。它一直导致 NullReferenceException。不知道是我的启动设置有问题还是怎么的，就是想不通。

System.NullReferenceException: 'Object reference not set to an instance of an object.'

我知道 Get access without a user 指南，我理解并可以开始工作，但我特别想使用 GetAccessTokenForAppAsync 方法，因为它会为我管理刷新令牌。否则，我将不得不在每次 API 调用时继续查询新令牌，并且不断生成有效令牌似乎是个坏主意。

Startup.cs ConfigureServices 方法：

public void ConfigureServices(IServiceCollection services)
{
    ...
    
    services.AddHttpClient();
    services.AddMicrosoftIdentityWebApiAuthentication(Configuration)
        .EnableTokenAcquisitionToCallDownstreamApi()
        // Use in-memory token cache
        // See https://github.com/AzureAD/microsoft-identity-web/wiki/token-cache-serialization
        .AddInMemoryTokenCaches();
        
    ...

}

Index.cshtml.cs。这是我打电话获取令牌的地方：

public class IndexModel : PageModel
{
    private readonly IHttpClientFactory _clientFactory;
    private readonly ITokenAcquisition _tokenAcquisition;

    public IndexModel(IHttpClientFactory clientFactory, ITokenAcquisition tokenAcquisition)
    {
        _clientFactory = clientFactory;
        _tokenAcquisition = tokenAcquisition;
    }

    public async Task OnGet()
    {
        // results in NullReferenceException
        string token = await _tokenAcquisition.GetAccessTokenForAppAsync("https://graph.microsoft.com/.default", tenant:"tenantId");
    }
}

appSettings.json。这些值由用户机密 json.

填充

{
  "AzureAd": {
    "Instance": "",
    "ClientId": "",
    "TenantId": "",
    "CallbackPath": "",
    "ClientSecret": "",
    "TimeoutInMinutes": ""
  },
  "ConnectionStrings": {
    "DefaultConnection": ""
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*"
}

Answer 1

首先，我已经成功重现了您的问题，如下所示：

你得到这个是因为 private readonly ITokenAcquisition _tokenAcquisition;

Note: This is actually a service which helps you to aquire access token on behalf of application. You cannot consume this service as constructor variable.

解法：

您应该按以下方式使用 ITokenAcquisition 服务：

   public async Task OnGet()
        {
            var _tokenAcquisition = this.HttpContext.RequestServices
                 .GetRequiredService<ITokenAcquisition>() as ITokenAcquisition;
            string token = await _tokenAcquisition.GetAccessTokenForAppAsync("https://graph.microsoft.com/.default", tenant: "tenantId");
        }

配置在Startup.cs

下

public void ConfigureServices(IServiceCollection services)
{
    string[] initialScopes = Configuration.GetValue<string>("DownstreamApi:Scopes")?.Split(' ');

    services.AddAuthentication(OpenIdConnectDefaults.AuthenticationScheme)
        .AddMicrosoftIdentityWebApp(Configuration.GetSection("AzureAd"))
        .EnableTokenAcquisitionToCallDownstreamApi(initialScopes)
        .AddMicrosoftGraph(Configuration.GetSection("DownstreamApi"))
        .AddInMemoryTokenCaches();

    services.AddControllersWithViews(options =>
    {
        var policy = new AuthorizationPolicyBuilder()
            .RequireAuthenticatedUser()
            .Build();
        options.Filters.Add(new AuthorizeFilter(policy));
    });
    services.AddRazorPages()
            .AddMicrosoftIdentityUI();
}

DownstreamApi 在appsettings.json下：

"DownstreamApi": {
    "BaseUrl": "https://graph.microsoft.com/v1.0",
    "Scopes": "https://graph.microsoft.com/.default"
  }

输出：

希望它能相应地解决您的问题。

如何修复调用 GetAccessTokenForAppAsync 以获取导致 NullReferenceException 的令牌？

How to fix calling GetAccessTokenForAppAsync to acquire token resulting in a NullReferenceException?

c#

bearer-token

asp.net-core

microsoft-graph-api