Interview Questions Azure AD B2C and OAuth You Should Be Ready For

As businesses expand into multi-channel platforms and applications, securing user access becomes increasingly complex. Azure AD B2C (Business-to-Consumer) is Microsoft’s identity management solution that supports authentication for external users such as customers or partners. Combine that with OAuth, one of the most widely adopted access protocols, and you’ve got a powerful security architecture.

If you’re preparing for an interview involving modern identity solutions, understanding Azure AD B2C, OAuth, identity federation, and single sign-on (SSO) is a must. This blog presents common interview questions you should expect — along with simple, practical answers to help you stand out.

Q1: What is Azure AD B2C, and how does it differ from Azure AD?

Answer: Azure AD B2C is a customer identity and access management (CIAM) solution that enables businesses to securely authenticate external users (like customers or partners). While Azure AD is designed for internal users in an organization (employees), Azure AD B2C is built for public-facing applications.

Azure AD B2C provides capabilities like:

• Social and local account sign-ins
• Custom branding of login pages
• Identity federation
• Integration with OAuth 2.0 and OpenID Connect
• Single sign-on across apps

Q2: What are common use cases for Azure AD B2C?

Answer:

• E-commerce platforms where users sign in with social accounts
• SaaS applications supporting external organizations
• Mobile or web apps requiring secure authentication for the public
• Multitenant apps with customizable branding for different clients

These scenarios make Azure AD B2C an ideal choice for managing external identities.

Q3: What is OAuth and why is it important?

Answer: OAuth (Open Authorization) is an open standard access protocol that allows an application to access resources on behalf of a user without exposing credentials. It’s widely used in modern identity systems, especially in web and mobile applications.

For example, when a user signs in with Google or Facebook to your app, OAuth helps grant access without sharing login credentials.

Q4: What’s the difference between OAuth 2.0 and OpenID Connect?

Answer: OAuth 2.0 is primarily an authorization framework, while OpenID Connect is an authentication layer built on top of OAuth 2.0.

• OAuth 2.0: Grants apps access to user resources (like files or calendar)
• OpenID Connect (OIDC): Verifies user identity and returns authentication details

Azure AD B2C supports both OAuth and OIDC, making it versatile for access and authentication use cases.

Q5: What are custom policies in Azure AD B2C?

Answer: Custom policies (Identity Experience Framework) are XML-based configurations that give you complete control over the behavior of sign-up, sign-in, password reset, and profile edit journeys in Azure AD B2C.

They are used when built-in policies (user flows) are not flexible enough — for example, when integrating with third-party IDPs or requiring multi-step verification logic.

Q6: How does identity federation work in Azure AD B2C?

Answer: Identity federation allows Azure AD B2C to authenticate users through external identity providers (IDPs) like Google, Facebook, LinkedIn, or enterprise providers like Azure AD or ADFS. This means users can log in using their existing credentials from another service.

Federation is implemented using standard access protocols like SAML, OAuth 2.0, and OpenID Connect.

Q7: How do you implement Single Sign-On (SSO) in Azure AD B2C?

Answer: Single sign-on (SSO) in Azure AD B2C is achieved when multiple apps use the same B2C tenant and share the same session. After a user logs in once, they can access other apps without re-authenticating (until the session expires).

To enable SSO:

• Register multiple apps under the same Azure AD B2C tenant
• Configure consistent redirect URIs
• Share cookies or tokens across domains
• Use consistent user flows or policies

Q8: Can you explain the OAuth 2.0 authorization code flow?

Answer: Yes. The authorization code flow is a secure method for web and mobile apps to obtain an access token. Here’s how it works:

• User is redirected to the authorization server (Azure AD B2C) to sign in.
• Upon successful login, the server sends an authorization code to the app.
• The app uses the code to request an access token from the token endpoint.
• The token is used to access protected resources.

This is the most secure flow, especially for apps running on servers.

Q9: What are access tokens, refresh tokens, and ID tokens?

Answer:

• Access Token: Used to access protected APIs or resources
• Refresh Token: Used to obtain new access tokens without user re-authentication
• ID Token: Contains information about the user (name, email, etc.), used in authentication

Azure AD B2C issues these tokens based on OAuth and OpenID Connect standards.

Q10: How do you secure OAuth tokens?

Answer:

• Use HTTPS to encrypt token transmission
• Store tokens securely (never in local storage for web apps)
• Implement token expiration and use refresh tokens securely
• Enable token revocation
• Use Proof Key for Code Exchange (PKCE) for mobile and public clients

These steps ensure your implementation of OAuth aligns with modern security practices.

Q11: How do you handle multi-tenancy in Azure AD B2C?

Answer: There are two common approaches:

• Single tenant with branding and policies for each customer
• Multiple B2C tenants for isolated customers

You can customize user flows and branding per tenant or domain. It’s crucial to plan tenant management, identity federation needs, and token issuance per customer segment.

Q12: What would you do if users report failed logins via social providers?

Answer:

• Check if the identity provider (Google, Facebook, etc.) is correctly configured
• Verify the app ID/secret and redirect URIs
• Review Azure AD B2C logs (diagnostic logs, App Insights)
• Ensure tokens are valid and scopes are correct
• Test with both mobile and desktop browsers

Troubleshooting identity federation and OAuth configuration is a common real-world skill.

Conclusion

Whether you’re working on a public-facing web app, mobile service, or an enterprise multi-tenant platform, understanding Azure AD B2C and OAuth is essential. These technologies power secure, flexible identity systems using open access protocols, identity federation, and support for single sign-on.

For interviews, focus on explaining concepts clearly, relate them to use cases, and demonstrate a practical grasp of how to implement and troubleshoot identity solutions. With the questions and answers provided above, you’ll be well-equipped to face even detailed technical discussions around Azure B2C and OAuth.