How to call custom authentication library method in Azure Function Startup? - .net-core

Question

I am trying to create an Azure Function (using NET 6.0 and Azure Functions runtime 4.0) and want to use a custom authentication library method AddAzureAdAuthentication that exists in my shared library just like how I was able to use it in this .Net Core api to authenticate api endpoints:
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc();
services.AddAzureAdAuthentication(Configuration);
services.AddCorsConfiguration(Configuration);
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
app.UseMiddleware(typeof(ErrorHandlingMiddleware));
app.UseCors("AllowSpecificOrigin");
app.UseAuthentication();
app.UseMvc();
}
}
I have read many articles and SO posts, but none gave a working solution to this problem. This is what I tried so far -
public override void Configure(IFunctionsHostBuilder builder)
{
var executionContextOptions = builder.Services.BuildServiceProvider()
.GetService<IOptions<ExecutionContextOptions>>().Value;
var currentDirectory = executionContextOptions.AppDirectory;
// Get the original configuration provider from the Azure Function
var configuration = builder.Services.BuildServiceProvider().GetService<IConfiguration>();
// Create a new IConfigurationRoot and add our configuration along with Azure's original configuration
Configuration = new ConfigurationBuilder()
.SetBasePath(currentDirectory)
.AddConfiguration(configuration) // Add the original function configuration
.AddJsonFile("local.settings.json", optional: false, reloadOnChange: true)
.Build();
// Replace the Azure Function configuration with our new one
builder.Services.AddSingleton(Configuration);
ConfigureServices(builder.Services);
}
private void ConfigureServices(IServiceCollection services)
{
services.AddAzureAdAuthentication(Configuration.GetSection("AzureAd"));
}
and my HttpTriggered Azure Function is a default function:
[FunctionName("TestADFunction")]
public static async Task<IActionResult> Run(
[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
ILogger log)
{
log.LogInformation("C# HTTP trigger function processed a request.");
string name = req.Query["name"];
string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
dynamic data = JsonConvert.DeserializeObject(requestBody);
name = name ?? data?.name;
string responseMessage = string.IsNullOrEmpty(name)
? "This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response."
: $"Hello, {name}. This HTTP triggered function executed successfully.";
return new OkObjectResult(responseMessage);
}
When I hit the function, it runs always without authenticating. I am not sure how to make this call to UseAuthentication();. I guess that is what is missing. Or, is there any other way to authenticate and authorize my azure function using my custom auth library?

Answer 1

To achieve the above requirements in your Function app , Need to add nuget package called Microsoft.Identity.Web
And in startup.cs we can use the below sample code:
[assembly: FunctionsStartup(typeof(FunctionsAuthentication.Startup))]
namespace FunctionsAuthentication
{
public class Startup : FunctionsStartup
{
public override void Configure(IFunctionsHostBuilder builder)
{
// This is configuration from environment variables, settings.json etc.
var configuration = builder.GetContext().Configuration;
builder.Services.AddAuthentication(sharedOptions =>
{
sharedOptions.DefaultScheme = "Bearer";
sharedOptions.DefaultChallengeScheme = "Bearer";
})
.AddMicrosoftIdentityWebApi(configuration)
.EnableTokenAcquisitionToCallDownstreamApi()
.AddInMemoryTokenCaches();
}
}
}
And in local settings.json we need to provide the credentials of our Azure AD
{
"IsEncrypted": false,
"Values": {
"AzureWebJobsStorage": "UseDevelopmentStorage=true",
"FUNCTIONS_WORKER_RUNTIME": "dotnet",
"AzureAd:Instance": "https://login.microsoftonline.com/",
"AzureAd:Domain": "<your_domain>",
"AzureAd:TenantId": "<your_tenant_id>",
"AzureAd:ClientId": "<client_id>",
"AzureAd:ClientSecret": "<client_secret>"
}
}
For complete setup please refer to this Blog