Add TenantId configuration instruction to Azure AD B2C docs

[Copilot]

The AzureADB2C appsettings.json example included a TenantId field but the accompanying instructions had no corresponding bullet explaining what value to use, leaving readers uncertain whether it duplicates ClientId or requires a separate value.

Changes

• aspnetcore/security/authentication/azure-ad-b2c.md: Added a TenantId bullet to the configuration instructions, directing users to the Tenant ID. Used instructions on where to find tenant ID from: https://learn.microsoft.com/en-us/azure/active-directory-b2c/tenant-management-read-tenant-name#get-your-tenant-id

Before:

* For Domain, use the domain of your Azure AD B2C tenant.
* For ClientId, use the Application (client) ID from the app registration you created in your tenant.
* For Instance, use the domain of your Azure AD B2C tenant.
* For SignUpSignInPolicyId, use the user flow policy defined in the Azure B2C tenant

After (new bullet added):

* For TenantId, use the **Tenant ID** from your Azure AD B2C tenant. In the Azure portal, search for and select **Microsoft Entra ID**. In the **Overview**, copy the **Tenant ID**.

Original prompt

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This section details on the original issue you should resolve

<issue_title>B2C Instructions show ClientId and TenantId as '999...' without instructions for TenantId</issue_title>
<issue_description>The JSON example shows this:

 "AzureAdB2C": {
    "Instance": "https://fabrikamb2c.b2clogin.com",
    "Domain": "fabrikamb2c.onmicrosoft.com",
    "ClientId": "99999999-9999-9999-9999-999999999999",
    "TenantId": "99999999-9999-9999-9999-999999999999",
    "SignedOutCallbackPath ": "/signout-callback-oidc",
    "SignUpSignInPolicyId": "your-user-flow"
  },

And the instructions read this:

For Domain, use the domain of your Azure AD B2C tenant.
For ClientId, use the Application (client) ID from the app registration you created in your tenant.
For Instance, use the domain of your Azure AD B2C tenant.
For SignUpSignInPolicyId, use the user flow policy defined in the Azure B2C tenant
Leave all other values as they are.

No mention of TenantId.

So, it's unclear what to put in the TenantId. Is this supposed to be a duplicate of the ClientId? Certainly, it can't be all 9's.

If not a duplicate, then where do we get it?

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Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 765e611b-a170-db1a-fa50-2771d79b2732
• Version Independent ID: ef34ebdf-977a-b797-e263-cb32c1643272
• Content: Cloud authentication with Azure Active Directory B2C in ASP.NET Core
• Content Source: aspnetcore/security/authentication/azure-ad-b2c.md
• Product: aspnet-core
• Technology: aspnetcore-security
• GitHub Login: @CamSoper
• Microsoft Alias: casoper</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes B2C Instructions show ClientId and TenantId as '999...' without instructions for TenantId #25034

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aspnetcore/security/authentication/azure-ad-b2c.md	Cloud authentication with Azure Active Directory B2C in ASP.NET Core

[wadepickett]

Looks good! Approved. I did make some suggetion for a couple little thins like a typo here and there original to the doc.