Blazor.BFF.AzureB2C.Template
This template can be used to create a Blazor WASM application hosted in an ASP.NET Core Web app using Azure B2C and Microsoft.Identity.Web to authenticate using the BFF security architecture. (server authentication) This removes the tokens from the browser and uses cookies with each HTTP request, response. The template also adds the required security headers as best it can for a Blazor application.
Features
- WASM hosted in ASP.NET Core 8
- BFF with Azure B2C using Microsoft.Identity.Web
- OAuth2 and OpenID Connect OIDC
- No tokens in the browser
- Azure AD Continuous Access Evaluation CAE support
Other templates
Using the template
install
dotnet new install Blazor.BFF.AzureB2C.Template
run
dotnet new blazorbffb2c -n YourCompany.Bff
Use the -n or --name parameter to change the name of the output created. This string is also used to substitute the namespace name in the .cs file for the project.
Setup after installation
Add the Azure B2C App registration settings
"AzureB2C": {
"Instance": "https://--your-domain--.b2clogin.com",
"Domain": "[Enter the domain of your B2C tenant, e.g. contoso.onmicrosoft.com]",
"TenantId": "[Enter 'common', or 'organizations' or the Tenant Id (Obtained from the Azure portal. Select 'Endpoints' from the 'App registrations' blade and use the GUID in any of the URLs), e.g. da41245a5-11b3-996c-00a8-4d99re19f292]",
"ClientId": "[Enter the Client Id (Application ID obtained from the Azure portal), e.g. ba74781c2-53c2-442a-97c2-3d60re42f403]",
"ClientSecret": "[Copy the client secret added to the app from the Azure portal]",
"ClientCertificates": [
],
// the following is required to handle Continuous Access Evaluation challenges
"ClientCapabilities": [ "cp1" ],
"CallbackPath": "/signin-oidc"
// Add your policy here
"SignUpSignInPolicyId": "B2C_1_signup_signin",
"SignedOutCallbackPath": "/signout-callback-oidc"
},
Add the permissions for Microsoft Graph if required, application scopes are used due to Azure B2C
"GraphApi": {
// Add the required Graph permissions to the Azure App registration
"TenantId": "[Enter 'common', or 'organizations' or the Tenant Id (Obtained from the Azure portal. Select 'Endpoints' from the 'App registrations' blade and use the GUID in any of the URLs), e.g. da41245a5-11b3-996c-00a8-4d99re19f292]",
"ClientId": "[Enter the Client Id (Application ID obtained from the Azure portal), e.g. ba74781c2-53c2-442a-97c2-3d60re42f403]",
"Scopes": ".default"
//"ClientSecret": "--in-user-secrets--"
},
Use Continuous Access Evaluation CAE with a downstream API (access_token)
Azure app registration manifest
"optionalClaims": {
"idToken": [],
"accessToken": [
{
"name": "xms_cc",
"source": null,
"essential": false,
"additionalProperties": []
}
],
"saml2Token": []
},Any API call for the Blazor WASM could be implemented like this:
[HttpGet]
public async Task<IActionResult> Get()
{
try
{
// Do logic which calls an API and throws claims challenge
// WebApiMsalUiRequiredException. The WWW-Authenticate header is set
// using the OpenID Connect standards and Signals spec.
}
catch (WebApiMsalUiRequiredException hex)
{
var claimChallenge = WwwAuthenticateParameters
.GetClaimChallengeFromResponseHeaders(hex.Headers);
return Unauthorized(claimChallenge);
}
}
The downstream API call could be implemented something like this:
public async Task<T> CallApiAsync(string url)
{
var client = _clientFactory.CreateClient();
// ... add bearer token
var response = await client.GetAsync(url);
if (response.IsSuccessStatusCode)
{
var stream = await response.Content.ReadAsStreamAsync();
var payload = await JsonSerializer.DeserializeAsync<T>(stream);
return payload;
}
// You can check the WWW-Authenticate header first, if it is a CAE challenge
throw new WebApiMsalUiRequiredException($"Error: {response.StatusCode}.", response);
}
Use Continuous Access Evaluation CAE in a standalone app (id_token)
Azure app registration manifest
"optionalClaims": {
"idToken": [
{
"name": "xms_cc",
"source": null,
"essential": false,
"additionalProperties": []
}
],
"accessToken": [],
"saml2Token": []
},If using a CAE Authcontext in a standalone project, you only need to challenge against the claims in the application.
private readonly CaeClaimsChallengeService _caeClaimsChallengeService;
public AdminApiCallsController(CaeClaimsChallengeService caeClaimsChallengeService)
{
_caeClaimsChallengeService = caeClaimsChallengeService;
}
[HttpGet]
public IActionResult Get()
{
// if CAE claim missing in id token, the required claims challenge is returned
var claimsChallenge = _caeClaimsChallengeService
.CheckForRequiredAuthContextIdToken(AuthContextId.C1, HttpContext);
if (claimsChallenge != null)
{
return Unauthorized(claimsChallenge);
}
uninstall
dotnet new uninstall Blazor.BFF.AzureB2C.Template
Development
build
https://docs.microsoft.com/en-us/dotnet/core/tutorials/create-custom-template
nuget pack content/Blazor.BFF.AzureB2C.Template.nuspec
install developement
Locally built nupkg:
dotnet new install Blazor.BFF.AzureB2C.Template.3.0.0.nupkg
Local folder:
dotnet new install <PATH>
Where <PATH> is the path to the folder containing .template.config.
Azure App registrations documentation
https://docs.microsoft.com/en-us/azure/active-directory-b2c/tutorial-register-applications
Credits, Used NuGet packages + ASP.NET Core 8.0 standard packages
- NetEscapades.AspNetCore.SecurityHeaders
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