Azure B2C Application call Azure AD API

Brandon Weber 6 Reputation points

I also have an Azure AD tenant (Tenant 1) with an application registered that is providing authentication for a Web API in the same tenant.

I have a web application that I want to support user signup/signin and registration via Azure B2C (Tenant 2) that needs to call the Web API in Tenant 1.

I have both of these applications setup as multi-tenant. I cannot seem to figure out how to configure my applications and successful make the call to the API.

Web App Settings:

"AzureAd": {
    "Instance": "",
    "Domain": "",
    "ClientId": "<Client ID of Web App in Tenant 2>",
    "ClientSecret": "<Client Secret of Web App in Tenant 2>",
    "SignedOutCallbackPath": "/signout/B2C_1_susi",
    "SignUpSignInPolicyId": "b2c_1_susi",
    "ResetPasswordPolicyId": "b2c_1_reset",
    "EditProfilePolicyId": "b2c_1_edit_profile",
    "CallbackPath": "/signin-oidc"
  "TodoList": {
    "TodoListAppId": "<Application ID of Web API in Tenant 1>",
    "TodoListScope": "api://MyAPI/.default",
    "TodoListBaseAddress": "https://localhost:44351",
    "AdminConsentRedirectApi": "https://localhost:44351/api/Home"

Startup Config of Web App:

                    .EnableTokenAcquisitionToCallDownstreamApi(new string[] { Configuration["TodoList:TodoListScope"] })

API App Settings:

"AzureAd": {
    "Instance": "",
    "Domain": "<Domain of Tenant 1>",
    "TenantId": "common",
    "ClientId": "<Client ID of Tenant 1>"

Startup Config of API:

Trying to sign in, I get this error: "Message contains error: 'invalid_request', error_description: 'AADB2C90117: The scope 'api://ApiTestApp/.default' provided in the request is not supported."

If I remove the EnableTokenAcquisitionToCallDownstreamApi, I can successfully sign in.

I have not found a way to add the API app in Tenant 1 as a permission to the web app in Tenant 2.

Is there anything I am missing? Is this even possible?

Microsoft Entra External ID
Microsoft Entra External ID
A modern identity solution for securing access to customer, citizen and partner-facing apps and services. It is the converged platform of Azure AD External Identities B2B and B2C. Replaces Azure Active Directory External Identities.
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Microsoft Entra ID
Microsoft Entra ID
A Microsoft Entra identity service that provides identity management and access control capabilities. Replaces Azure Active Directory.
20,218 questions
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  1. JamesTran-MSFT 36,516 Reputation points Microsoft Employee

    @Brandon Weber
    Thank you for the follow up and I apologize for the delayed response!

    When it comes to the Set up sign-in for multi-tenant Azure Active Directory using custom policies in Azure Active Directory B2C documentation, I tested this out in my own environment and will post my findings below.

    Based off my testing, you should be able to sign-in to your application with any Azure B2C user. However, if you sign-in with a user from your AzureAD tenant, you'll need to use the "social account button" and you'll be prompted to enter a verification code before signing in.


    If you have any other questions or would like us to take a closer look into your environment, please let me know.
    Thank you again for your time and patience throughout this issue!


    Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.