Adding a batch request step should not authenticate the request

[olivermue]

Is your feature request related to a problem? Please describe the problem.

Recently I created through the SDK a batch request to receive the members and owners of a bunch of group ids. During testing, I noticed that adding all these requests to the batch takes a relatively long time.

After some digging into the code I found the root source to be the call to RequestAdapter.ConvertToNativeRequestAsync<HttpRequestMessage>() which will call AuthenticateRequestAsync() of the given authentication provider. This is not needed, cause the token on the individual request will be ignored and not being serialized into the batch step information.

Describe the solution you'd like.

To solve this issue I created an intermediate service client with my own do nothing authentication provider, used that to create the native request and added it via AddBatchRequestStep(). After doing so, the loop with 200 requests dropped from 300ms down to 1ms:

private class DoNothingAuthenticationProvider : IAuthenticationProvider
{
    public static readonly IAuthenticationProvider Default = new DoNothingAuthenticationProvider();

    public Task AuthenticateRequestAsync(
        RequestInformation request,
        Dictionary<string, object>? additionalAuthenticationContext = null,
        CancellationToken cancellationToken = default)
    {
        return Task.CompletedTask;
    }
}

var noAuthServiceClient = new GraphServiceClient(DoNothingAuthenticationProvider.Default);

var membersRequest = serviceClient.Groups[groupId].Members.ToGetRequestInformation();
var nativeRequest = await noAuthServiceClient.RequestAdapter.ConvertToNativeRequestAsync<HttpRequestMessage>(membersRequest);
batch.AddBatchRequestStep(new BatchRequestStep($"{groupId}|members", nativeRequest));

Additional context?

To make it easier to reproduce the problem, here is some sample code that shows how AddBatchRequestStepAsync() internally calls the authentication validator:

private class SlowAuthenticationProvider : IAuthenticationProvider
{
    public async Task AuthenticateRequestAsync(
        RequestInformation request,
        Dictionary<string, object>? additionalAuthenticationContext = null,
        CancellationToken cancellationToken = default)
    {
        Console.WriteLine("Trying to authenticate request...");
        await Task.Delay(100, cancellationToken);
    }
}

public static async Task Main()
{
    var authProvider = new SlowAuthenticationProvider();
    var serviceClient = new GraphServiceClient(authProvider);
    var batch = new BatchRequestContentCollection(serviceClient);

    var membersRequest = serviceClient.Groups["abc"].Members.ToGetRequestInformation();
    // Calls the authentication provider (can't be avoided IMHO)
    var nativeRequest = await serviceClient.RequestAdapter.ConvertToNativeRequestAsync<HttpRequestMessage>(membersRequest);
    batch.AddBatchRequestStep(new BatchRequestStep("abc|members", nativeRequest));

    // Calls the authentication provider (could be avoided IMHO)
    await batch.AddBatchRequestStepAsync(membersRequest);
}