How can Contoso ensure that Fabrikam developers use their existing credentials to access resources in the Azure subscription?

In order for Fabrikam developers to use their existing credentials to access resources in the Azure subscription owned by Contoso, adding the developers as guest users in Azure Active Directory (Azure AD) is the most effective approach. By inviting these developers as guest users, they can authenticate using their own credentials from their home organization, allowing seamless access to the resources in Contoso's Azure subscription.

This method leverages Azure AD's built-in B2B (Business-to-Business) collaboration capabilities, which are specifically designed to enable external users to utilize their existing identity with minimal friction. As guest users, the developers will have access to shared resources in a secure manner, yet still retain the identity management controls established by Contoso.

In contrast, configuring B2B collaboration generally encompasses the process of adding guest users, making this option less specific. Creating a separate Azure AD tenant would not help the developers use their existing credentials, as they would need to create new accounts in the new tenant. Setting up Azure AD external identities could facilitate access but is more complex and may not directly fulfill the requirement of using existing credentials as efficiently as simply adding the developers as guest users.