Trying to connect to MS Graph API from an Azure Fn Project

I'm trying to create a new az fn in an existing project.... I need this new fn to query Graph Api under the hood.

The following code is not working because it can't find the package / library for DelegateAuthenticationProvider class:

       string[] scopes = new[] { "https://graph.microsoft.com/.default" };

        var confidentialClientApplication = ConfidentialClientApplicationBuilder
                    .Create(ApplicationClientID)
                    .WithTenantId(AzureTenantID)
                    .WithClientSecret(ApplicationClientSecret)
                    .Build();

        // Build the Microsoft Graph client. As the authentication provider, set an async lambda
        // which uses the MSAL client to obtain an app-only access token to Microsoft Graph,
        // and inserts this access token in the Authorization header of each API request. 
        GraphServiceClient graphServiceClient =
            new GraphServiceClient(new Microsoft.Graph.DelegateAuthenticationProvider(async (requestMessage) => {

                    // Retrieve an access token for Microsoft Graph (gets a fresh token if needed).
                    var authResult = await confidentialClient
                        .AcquireTokenForClient(scopes)
                        .ExecuteAsync();

                    // Add the access token in the Authorization header of the API request.
                    requestMessage.Headers.Authorization = 
                        new AuthenticationHeaderValue("Bearer", authResult.AccessToken);
                })
            );

Here's the project file contents:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <AzureFunctionsVersion>v4</AzureFunctionsVersion>
    <RootNamespace>widgets</RootNamespace>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Azure.Identity" Version="1.9.0" />
    <PackageReference Include="Azure.Security.KeyVault.Secrets" Version="4.5.0" />
    <PackageReference Include="Microsoft.Azure.KeyVault" Version="3.0.5" />
    <PackageReference Include="Microsoft.Graph" Version="5.18.0" />
    <PackageReference Include="Microsoft.Graph.Core" Version="3.0.9" />
    <PackageReference Include="Microsoft.Identity.Client" Version="4.54.1" />
    <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="4.1.1" />
    <PackageReference Include="Microsoft.Azure.Services.AppAuthentication" Version="1.6.0" />
  </ItemGroup>
  <ItemGroup>
    <None Update="host.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="local.settings.json">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
      <CopyToPublishDirectory>Never</CopyToPublishDirectory>
    </None>
  </ItemGroup>
</Project>

I added the following dependencies to support this call to graph:

<PackageReference Include="Microsoft.Graph" Version="5.18.0" />
<PackageReference Include="Microsoft.Graph.Core" Version="3.0.9" />
<PackageReference Include="Microsoft.Identity.Client" Version="4.54.1" />

It's my understanding that DelegateAuthenticationProvider class is a part of Graph.Core.

Hopefully it's something super simple I've missed. Any tips would be appreciated.

The way you are trying to do it seems deprecated since Version 3 of the Microsoft.Graph.Core package. Here you find the migration description.

As it seems you are trying to authenticate via ClientSecret, I think this is the documentation you are looking for.

Code from the documentation:

// The client credentials flow requires that you request the
// /.default scope, and pre-configure your permissions on the
// app registration in Azure. An administrator must grant consent
// to those permissions beforehand.
var scopes = new[] { "https://graph.microsoft.com/.default" };

// Values from app registration
var clientId = "YOUR_CLIENT_ID";
var tenantId = "YOUR_TENANT_ID";
var clientSecret = "YOUR_CLIENT_SECRET";

// using Azure.Identity;
var options = new ClientSecretCredentialOptions
{
    AuthorityHost = AzureAuthorityHosts.AzurePublicCloud,
};

// https://learn.microsoft.com/dotnet/api/azure.identity.clientsecretcredential
var clientSecretCredential = new ClientSecretCredential(
    tenantId, clientId, clientSecret, options);

var graphClient = new GraphServiceClient(clientSecretCredential, scopes);