How to configure Azure AD authentication in Hybrid ASP.NET Core MVC (backend) and Vuejs SPA (frontend)? - vue.js

Question

My application is a hybrid approach where use ASP.NET Core MVC as my backend. I have various controllers which my front end uses to pull data from our database and also to do API calls on MS Graph. I am using the following program.cs file to get the authentication initiated when a user first logs on to the site:
//authentication pipline
builder.Services.AddHttpContextAccessor();
var initialScopes = builder.Configuration.GetValue<string>("DownstreamApi:Scopes")?.Split(' ');
builder.Services.AddAuthentication(OpenIdConnectDefaults.AuthenticationScheme)
.AddMicrosoftIdentityWebApp(options =>
{
builder.Configuration.Bind("AzureAd", options);
options.Events = new OpenIdConnectEvents
{
//Tap into this event to add a UserID Claim to a new HttpContext identity
OnTokenValidated = context =>
{
//This query returns the UserID from the DB by sending the email address in the claim from Azure AD
string query = "select dbo.A2F_0013_ReturnUserIDForEmail(#Email) as UserID";
string connectionString = builder.Configuration.GetValue<string>("ConnectionStrings:DBContext");
string signInEmailAddress = context.Principal.FindFirstValue("preferred_username");
using (var connection = new SqlConnection(connectionString))
{
var queryResult = connection.QueryFirst(query, new { Email = signInEmailAddress });
var claims = new List<Claim>
{
new Claim("UserID", queryResult.UserID.ToString())
};
var appIdentity = new ClaimsIdentity(claims);
context.Principal.AddIdentity(appIdentity);
}
return Task.CompletedTask;
},
};
}).EnableTokenAcquisitionToCallDownstreamApi(initialScopes)
.AddMicrosoftGraph(builder.Configuration.GetSection("DownstreamApi"))
.AddInMemoryTokenCaches();
//Add Transient Services
builder.Services.AddTransient<IOneDrive, OneDrive>();
builder.Services.AddControllers(options =>
{
var policy = new AuthorizationPolicyBuilder()
.RequireAuthenticatedUser()
.Build();
options.Filters.Add(new AuthorizeFilter(policy));
}).AddMicrosoftIdentityUI();
builder.Services.AddRazorPages().AddRazorPagesOptions(options =>
{
options.Conventions.AllowAnonymousToFolder("/Login");
options.Conventions.AuthorizeFolder("/");
options.Conventions.AuthorizeFolder("/files");
}).AddMicrosoftIdentityUI();
// Add the UI support to handle claims challenges
builder.Services.AddServerSideBlazor()
.AddMicrosoftIdentityConsentHandler();
builder.Services.AddRequiredScopeAuthorization();
In the Azure AD portal my application is registered as a web app. So when a user initially goes to the site they are redirected to https://login.microsoftonline.com/blahblah to get the login process started. This is automated by the Azure AD identity platform. Then once the login occurs they are redirected to localhost where the VueJS spa is loaded (localhost:43862). My spa uses various axios requests to the controllers and they pull data and vue router loads components. However, my issue is say the user needs to relog in because the cookie is expired or they logged out in another tab. The next axios request made by the expired session does not redirect the user to Azure login screen but instead results in an CORS error. So I need to get my axios requests to force the page redirect to Azure AD login screen (which probably is the worst idea since CORS policy is resulting in error) or have it return a redirect to localhost/login which is my own custom login screen with a button to Azure AD login and shouldnt impact CORS. So how do I intercept this Azure AD redirect to Azure AD login and replace with my own?
I have also tried to return a 401 error code so I could check for that in my axios request but to no avail it does nothing. If I put a breakpoint there it does hit this code but it does not change the status code of the response and I still get 302. My code for that was to try and add to the event :
OnRedirectToIdentityProvider = context =>
{
context.Response.StatusCode = 401;
return Task.CompletedTask;
}
My other ideas was maybe I should set my CORS policy to allow redirects from login.microsoft.com? Or would this be bad practice?

Answer 1

I can answer part of your question... First, for our API application which is protected by Azure AD, what the API should do is validating the request whether it contained a correct access token in the request header, if yes, give the response, if no, then give error like 401 or 403. A normal API application shouldn't have a UI to let users sign in. Anyway, if you want to expose an API in an MVC project, it's OK, but for API itself, it shouldn't have a UI.
Let's see sample below, I had a .net 6 web api project, and here's my program.cs:
using Microsoft.Identity.Web;
var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
builder.Services.AddMicrosoftIdentityWebApiAuthentication(builder.Configuration);
builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
var app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
app.UseSwagger();
app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers();
app.Run();
And it requires configurations in appsetting.json.
"AzureAd": {
"Instance": "https://login.microsoftonline.com/",
"ClientId": "azure_ad_client_id",
"ClientSecret": "client_secret",
"Domain": "tenant_id",
"TenantId": "tenant_id",
//"Audience": "api://azure_ad_client_id_which exposed_api" // here I used the same azure ad app to expose API, so I can comment this property
},
And this is the Controller：
[ApiController]
[Route("[controller]")]
[Authorize]
public class WeatherForecastController : ControllerBase
{
[RequiredScope("Tiny.Read")]
[HttpGet]
public string Get()
{
return "world";
}
}
I had an Azure AD app, and I exposed an API like this:
I also add this API for the same Azure AD app.
Then let's do a test. When I call this API directly, I will get 401 error:
If I used an expired token within the request, I will also get 401 error:
But if I used a correct token(go to https://jwt.io to decode the token, we should see it containing correct scope, for me its "scp": "Tiny.Read",), I will get response:
And till now, the API part had finished. Let's see the client SPA. For SPA, you should integrate MSAL so that you can make your users to sign in via Azure AD, and generate the access token for calling MS graph API or your own API. The code for generating access token should be the same but you should set different scope for different API. In my scenario, my API required a scope Tiny.Read, then I should set in my client App.
Here's an screenshot for generating access token in react. You need to set the scope in your code.
Now you have the method to generate access token, you already know the API url. Then you can send request to call api, using AJAX, using fetch, or something else, sending an http request is ok. And in the calling api part, you also need to handle the response. If the response code is 401, then you need to do some logic, maybe redirect to the sign in page. And you said you had trouble here, you met CORS issue. I can't answer this part. I think it depends on how you redirect to Azure AD sign in page. I'm afraid you can take a look at this sample to learn how to sign in users and call graph api.