Azure AD B2C to Entra External ID (EEID) Migration Kit — Attribute Mapping

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You can see the whole series in this list.

The repo. is here.

One feature of the migration kit is that it allows you to rename/map attributes.

As per the docs.

AttributeMappings

Maps source attribute names to different target names.

Key = source attribute name in B2C
Value = target attribute name in External ID

Example:
...
"AttributeMappings": {
  "extension_b2c_app_LegacyCustomerId": "extension_extid_app_CustomerId",
  "extension_b2c_app_Department": "extension_extid_app_DepartmentCode"
}

Behavior:

• If attribute is in mappings: rename it to target name
• If attribute is NOT in mappings: copy as-is (same name)
• All attributes not explicitly mapped or excluded are copied unchanged

Ensure all the target custom attributes exist in your EEID tenant.

This is under “External Identities / Custom user attributes”.

Create all the custom attributes you map.

Note that you need to remove all hyphens from the GUID part of the extension attribute name.

“1abd7936f-dccb-8e6d-b956–3277de870f8c” becomes:

“1abd7936fdccb8e6db9563277de870f8c”

and the full name is:

“extension_1abd7936fdccb8e6db9563277de870f8c_MFAType”

In my appsettings.json:

"Import": {
  "MigrationAttributes": [
    "RequireMigration",
    "OriginalTenantId",
    "MigrationDate",
    "LastSyncDate"
  ],
  "AttributeMappings": {
    "extension_51...4e_MFAType": "extension_1b...8c_MFAMethod"
  },

I’m mapping “MFAType” to “MFAMethod”.

For this to work, you have to add the extension attribute to the SelectFields option:

"Export": {
  "SelectFields": "id,userPrincipalName,displayName,givenName,surname,mail,
    identities,extension_51...4e_MFAType",
  "MaxUsers": null,
  "IncludeDeletedUsers": false,
  "EnableBatching": true
},

My B2C user shows:

"userType": "Member",
"identityParentId": null,
"agentIdentityBlueprintId": null,
"extension_51...4e_MFAType": "SMS",

After migration, my EEID user shows:

"userType": "Member",
"identityParentId": null,
"agentIdentityBlueprintId": null,
"extension_1b...8c_MFAMethod": "SMS",

You could have a long select list if you have many attributes, but it does work!

All good!