How does B2C determine user uniqueness?

Question

How does B2C determine user uniqueness (i.e. when to create a new user vs use an existing user)? What happens when a pre-existing b2c user last name changes due to marriage / divorce? Will the next B2C auth create a new user or update the last name for the existing user? How does IDP type affect this (AAD vs external customer IDP)?

Answer 1

Hello @ScottM , Please find below the answer to your questions:

How does B2C determine user uniqueness (i.e. when to create a new user vs use an existing user)?

Azure AD B2C first checks to see if ObjectID of the authenticating user exists in the directory or not.

• If the Object ID doesn't exist, sign-up process is initiated by using the LocalAccountSignUpWithLogonEmail technical profile.
• If the Object ID exists, AAD-UserReadUsingObjectId technical profile is used to fetch details of the user based on his/her object ID.

What happens when a pre-existing b2c user last name changes due to marriage / divorce? Will the next B2C auth create a new user or update the last name for the existing user?

Once the user completes the sign-up process in B2C, last name gets populated locally in B2C directory. If the last name gets changed in federated IDP (e.g. Facebook) afterwards, it will not be changed automatically in Azure AD B2C at subsequent sign-in. After signup, if user wants to change last name in B2C, he/she would need to edit profile which should trigger profile editing user flow in the backend.

How does IDP type affect this (AAD vs external customer IDP)?

The behavior explained in the answer of above question should be same for both Local Account signup and any External IDP that users may use to sign-up.

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