Initiate and store multiple OAuth2 external authentication challenges in a ASP.NET Core MVC application? - oauth-2.0

Question

I can authenticate against two separate OAuth authentication schemes but it seems only one can be active at a time. I'd like to compare data from two separate SaaS applications and therefore I need two separate Bearer tokens. How can I initiate multiple OAuth challenges when the user loads the application and then store the Bearer Tokens for each? (e.g. in the Context.User cookie?)
My Startup.cs is as follows:
public void ConfigureServices(IServiceCollection services)
{
services.AddRouting();
services.AddAuthentication(options =>
{
options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
})
.AddCookie(options =>
{
options.LoginPath = "/signin";
options.LogoutPath = "/signout";
})
.AddScheme1 (options =>
{
options.ClientId = Configuration["Scheme1:ClientId"];
options.ClientSecret = Configuration["Scheme1:ClientSecret"];
options.Scope.Add("scope1");
options.SaveTokens = true;
})
.AddScheme2(options =>
{
options.ClientId = Configuration["Scheme2:ClientId"];
options.ClientSecret = Configuration["Scheme2:ClientSecret"];
options.Scope.Add("scope1");
options.SaveTokens = true;
});...
}
The AuthenticationController calls the Challenge overloaded method from the Microsoft.AspNetCore.Mvc.Core assembly that takes a single provider/scheme (passing multiple schemes in the overloaded method seems to be ignored).
[HttpGet("~/signin")]
public async Task<IActionResult> SignIn() => View("SignIn", await HttpContext.GetExternalProvidersAsync());
[HttpPost("~/signin")]
public async Task<IActionResult> SignIn([FromForm] string provider)
{
...
return Challenge(new AuthenticationProperties { RedirectUri = "/" }, provider);
}
Presumably, you'd prompt the user to sign-into one external application, redirect back to the home page, and then prompt them to sign-into the second one, and then allow them to start using the application proper.
If this is possible - e.g. using a "multiple" Auth cookie - how then would I fetch the correct Bearer token and User values for the given scheme? Currently you just seem to fetch the token with a generic "access_token" name and unique user values:
string accessToken = await HttpContext.GetTokenAsync("access_token");
string userID = User.FindFirstValue(ClaimTypes.NameIdentifier);
There does seem to be some information here regarding using a SignInManager but I'm unable to determine if this is applicable to this problem.

Answer 1

I would aim to start with a standard architecture where the user authenticates with the one and only app, and gets only one set of tokens, issued by your own Authorization Server.
SaaS DATA - OPTION 1
Does the user need to get involved in these connections or can you use a back end to back end flow here?
Your C# code could connect to the SaaS provider with the client credentials grant, using the client ID and secret that you reference above. Provider tokens would then be cached in memory, then used by the back end code to return provider data to the UI. This is a simple option to code.
SaaS DATA - OPTION 2
If the user needs to get involved, because the data is owned by them, you might offer UI options like this. After each click the user is redirected again, to get a token for that provider.
View provider 1 data
View provider 2 data
Aim to emulate the embedded token pattern, where the provider tokens are available as a secondary credential. How you represent this could vary, eg you might prefer to store provider tokens in an encrypted cookie.
CODING AND SIMPLICITY
I would not mix up provider tokens with the primary OAuth mechanism of signing into the app and getting tokens via the .NET security framework, which typically implements OpenID Connect. Instead I would aim to code the SaaS connections on demand.
I think you will find it easier to code the SaaS connections with a library approach, such as Identity Model. This will also help you to deal with SaaS provider differences more easily.

Answer 2

I assume you use OIDC schemes.
First, you need to add two cookie schemes, one for each OIDC authentication scheme as their sign in scheme and set their callback path to different values to stop them competing:
services.AddAuthentication()
.AddCookie("Cookie1")
.AddCookie("Cookie2")
.AddOpenIdConnect("OidcScheme1", opt =>
{
opt.SignInScheme = "Cookie1";
opt.CallbackPath = "/signin-oidc-scheme1";
opt.SaveTokens = true;
})
.AddOpenIdConnect("OidcScheme2", opt =>
{
opt.SignInScheme = "Cookie2";
opt.CallbackPath = "/signin-oidc-scheme2";
opt.SaveTokens = true;
});
This will instruct the OIDC handler to authenticate the user from corresponding cookie.
Second, you need a controller action to challenge the user against each OIDC scheme:
[HttpGet]
[Route("login")]
[AllowAnonymous]
public IActionResult Login([FromQuery]string scheme,
[FromQuery]string? returnUrl)
{
return Challenge(new AuthenticationProperties
{
RedirectUri = returnUrl ?? "/"
}, scheme);
}
From your web app, you need to send the user to the Login endpoint twice with different scheme values:
GET /login?scheme=OidcScheme1
GET /login?scheme=OidcScheme2
Or chain them together using the returnUrl:
GET /login?scheme=OidcScheme1&returnUrl=%2Flogin%3Fscheme%3DOidcScheme2
Once signed in, there should be two cookies in the browser window, for example:
To authenticate the user and restore both identities from two cookies, you can use authorization policy:
[HttpGet]
[Authorize(AuthenticationSchemes = "OidcScheme1,OidcScheme2")]
public async Task<IActionResult> SomeOperation()
{
// Two identities, one from each cookie
var userIdentities = User.Identities;
...
}
To get access token from each authentication scheme, use the method you discovered (GetTokenAsync) and specify authentication scheme:
var token1 = await HttpContext.GetTokenAsync("OidcScheme1", "access_token");
var token2 = await HttpContext.GetTokenAsync("OidcScheme2", "access_token");
It is possible that the access token is not returned from the token endpoint depends on the response_type you used. If this is the case, try set the OpenIdConnectionOptions.ResponseType to OpenIdConnectResponseType.Code and make sure the scope is correct.

Answer 3

I encountered a similar problem where we had microservices that are/were shared across multiple products with each product having a separate IDP tenant (essentially a different token issuer). Perhaps a similar approach might work for your scenario...
The following link helped me with a solution - see here.
Basically I defined a smart authentication scheme
var builder = services.AddAuthentication(o =>
{
o.DefaultAuthenticateScheme = "smart";
//...
});
Then in the smart policy scheme definition, I decode the JWT coming in to work out the issuer from the iss claim in the JWT, so that I can forward to the correct location for JWT bearer authentication.
builder.AddPolicyScheme("smart", "smart", options =>
{
options.ForwardDefaultSelector = context =>
{
var jwtEncodedString = context.Request.Headers["Authorization"].FirstOrDefault()?.Substring(7);
if (string.IsNullOrEmpty(jwtEncodedString))
return settings.Tenants.First().Key; // There's no authorization header, so just return any.
var token = new JwtSecurityToken(jwtEncodedString: jwtEncodedString);
var issuer = token.Claims.First(c => c.Type == "iss").Value?.TrimEnd('/');
var tenant = settings.Tenants
.Where(pair => pair.Value.Issuer.TrimEnd('/') == issuer)
.Select(pair => pair.Key).FirstOrDefault();
if (tenant == null)
throw new AuthorizationException($"Failed to locate authorization tenant with issuer '{issuer}'.");
return tenant;
};
});
Note: settings.Tenants is just an array of whitelisted tenants (from appsettings) that I configure as follows:
foreach (var tenant in settings.Tenants)
builder.AddJwtBearer(tenant.Key, options => Configure(options, tenant.Value, defaultJwtBearerEvents));