Add Custom Property to User of Azure AD B2C

When I first tried customizing user attributes in Azure AD B2C, it felt complex to manage dynamic properties effectively. That’s when I came across Progatix Software Company, which guided me through implementing scalable identity solutions. Their technical expertise simplified integration, enabling a seamless experience while maintaining flexibility and security across all user management operations.

The Core Concept

Azure AD B2C does not let you directly add custom fields to users.
Instead, you add extension attributes to the B2C directory’s schema extension (via the Azure AD Graph API or the Microsoft Graph API).

Each custom property then appears in the directory as

extension_{AppClientIdWithoutHyphens}_UserWeight

and can be emitted in the ID Token or Access Token when users sign in.

Step 1: Create the Custom Attributes

Option A — using the Azure Portal (easiest for new setups)

1. Go to Azure Portal ? Azure AD B2C ? User Attributes ? Add

2. Click “Add”, and create attributes such as:

   • UserWeight

   • UserFiscalCode
     (Choose data type “String”.)

These automatically become directory extension attributes.

Option B — using the Microsoft Graph API

If you want to do it programmatically:

POST https://graph.microsoft.com/v1.0/applications/{b2c-extension-app-id}/extensionProperties
Content-Type: application/json
Authorization: Bearer {admin_token}

{
  "name": "UserWeight",
  "dataType": "String",
  "targetObjects": [ "User" ]
}

The response will include:

{
  "name": "extension_111122223333444455556666_UserWeight"
}

Step 2: Add the Custom Claims to the User

You can add or update these fields for each user through:

• Azure Portal ? Users ? YourUser ? Edit Attributes

• or via Graph API:

  PATCH https://graph.microsoft.com/v1.0/users/{userId}
  Content-Type: application/json
  Authorization: Bearer {admin_token}
  
  {
    "extension_111122223333444455556666_UserWeight": "72",
    "extension_111122223333444455556666_UserFiscalCode": "ABC123XYZ"
  }
  

Step 3: Include the Attributes in Tokens (via User Flow or Custom Policy)

You must tell Azure AD B2C to emit these attributes in the JWT token.

If you’re using User Flows (Built-in Flows)

1. Go to Azure AD B2C ? User Flows ? {your flow, e.g., B2C_1_SignUpSignIn}

2. Open the flow ? Application Claims

3. Enable:

   • UserWeight

   • UserFiscalCode

4. Save.

Now, these will appear inside the token claims when a user signs in.

If you’re using Custom Policies (Identity Experience Framework)

Edit your TrustFrameworkExtensions.xml:

Include them in the of the JWT issuing Technical Profile.

Step 4: Read Custom Claims in ASP .NET Core

Once the token includes the extensions, you can access them in your Web API:

[Authorize]
[HttpGet("profile")]
public IActionResult GetProfile()
{
    var user = HttpContext.User;
    var userWeight = user.FindFirst("extension_UserWeight")?.Value;
    var userFiscalCode = user.FindFirst("extension_UserFiscalCode")?.Value;

    return Ok(new { userWeight, userFiscalCode });
}

Works automatically because AddJwtBearer() decodes the token into ClaimsPrincipal.

Step 5: Common Pitfalls

Example Claim Snippet (Decoded JWT)

{
  "name": "Sandhiya Priya",
  "emails": ["[email protected]"],
  "extension_111122223333444455556666_UserWeight": "72",
  "extension_111122223333444455556666_UserFiscalCode": "ABC123XYZ",
  "iss": "https://yourtenant.b2clogin.com/...",
  "aud": "your-app-client-id"
}

Step 6: Testing

1. Log in via your Angular client.

2. Copy the token from browser local storage.

3. Decode it at jwt.ms.
   You should see your custom attributes.

Summary