How to Unit test or Mock DefaultAzureCredential Method

[PrakashRajanSakthivel]

I am using DefaultAzureCredential to fetch the access token in my function app which has managed identity from azure to authenticate itself to the APIM. so I am using a HttpMessageHandler in that I am checking If the token doesnt exist make a call to Azure and get the token.

Startup in the Function App

public override void Configure(IFunctionsHostBuilder builder)
{
 builder.Services.AddHttpClient(AppConstants.ReplyService)
 //Adding token handler middleware to add authentication related details.
 .AddHttpMessageHandler<AccessTokenHandler>();
}

Handler File:

protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
 {
 // Use the token to make the call.
 // other details
 request.Headers.Authorization = new AuthenticationHeaderValue(AppConstants.AuthHeader, await GetToken());
  return await base.SendAsync(request, cancellationToken);
 }
 
private async Task<string> GetToken(bool needsRefresh = false)
{
 if (accessTokenCache.GetCount() == 0 || needsRefresh)
 {
  var tokenCredential = new DefaultAzureCredential();
  var accessToken = await tokenCredential.GetTokenAsync(
  new TokenRequestContext(scopes: new string[] { _config["AppId"] + "/.default" }) { });
   accessTokenCache.Set("accessToken", accessToken.Token, DateTimeOffset.Now.AddMinutes(55));
     }
     return accessTokenCache.Get("accessToken")?.ToString() ?? throw new Exception("Unable to Fetch Access Token from Cache");
    }

Is there any way I can inject the new AzureDefaultCredentail Method so that I can mock it or pass on like IHttpClientFactory to inject it? I dont find much reference on the unit testin part

[jsquire]

Thank you for your feedback. Tagging and routing to the team members best able to assist.

[christothes]

Hi @PrakashRajanSakthivel - If you need to mock DefaultAzureCredential, I'd recommend something like Moq. For example:

var dacMock = new Mock<DefaultAzureCredential>();
int i = 0;
dacMock
    .Setup(m => m.GetToken(It.IsAny<TokenRequestContext>(), It.IsAny<CancellationToken>()))
    .Callback (() => i++);

var dac = dacMock.Object;
dac.GetToken(new TokenRequestContext());
Console.WriteLine(i.ToString());

[ghost]

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[PrakashRajanSakthivel]

Thanks, @christothes , Is that something I can inject into my class so that it gets picked up? like in my example above

protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
 {
 // Use the token to make the call.
 // other details
 request.Headers.Authorization = new AuthenticationHeaderValue(AppConstants.AuthHeader, await GetToken());
  return await base.SendAsync(request, cancellationToken);
 }

private async Task<string> GetToken(bool needsRefresh = false)
{
 if (accessTokenCache.GetCount() == 0 || needsRefresh)
 {
// Instead of creating a new instance?
  var tokenCredential = new DefaultAzureCredential();
  var accessToken = await tokenCredential.GetTokenAsync(
  new TokenRequestContext(scopes: new string[] { _config["AppId"] + "/.default" }) { });
   accessTokenCache.Set("accessToken", accessToken.Token, DateTimeOffset.Now.AddMinutes(55));
     }
     return accessTokenCache.Get("accessToken")?.ToString() ?? throw new Exception("Unable to Fetch Access Token from Cache");
    }

[christothes]

As long as it gets invoked sometime before you attempt to call GetToken, it would be up to you how to call it. In my simple repro, I just called it at the beginning of the function invoke. Since it is static it does not need to be injected.

[ghost]

Hi, we're sending this friendly reminder because we haven't heard back from you in 7 days. We need more information about this issue to help address it. Please be sure to give us your input. If we don't hear back from you within 14 days of this comment the issue will be automatically closed. Thank you!