how to check if user exists in AD before migration - azure-ad-b2c

Question

I'm using the guide here to perform Just-In-Time migration of a user from a legacy Idp to azure ad b2c: https://github.com/azure-ad-b2c/user-migration/tree/master/jit-migration-v2. I have this working properly on its own with a service I am using to query the legacy IdP and returning expected claims.
However, I would like to modify the above to first check if the user exists in AD before trying to migrate. I have tried declaring a ValidationTechnicalProfile, but it doesn't really seem to be working:
<TechnicalProfile Id="AAD-UserCheckUsingEmailAddress">
<Metadata>
<Item Key="Operation">Read</Item>
<Item Key="RaiseErrorIfClaimsPrincipalDoesNotExist">true</Item>
<Item Key="UserMessageIfClaimsPrincipalDoesNotExist">An account could not be found for the provided user ID.</Item>
</Metadata>
<IncludeInSso>false</IncludeInSso>
<InputClaims>
<InputClaim ClaimTypeReferenceId="signInName" PartnerClaimType="username" Required="true" />
</InputClaims>
<OutputClaims>
<!-- Required claims -->
<OutputClaim ClaimTypeReferenceId="objectId" />
</OutputClaims>
<IncludeTechnicalProfile ReferenceId="AAD-Common" />
</TechnicalProfile>
Below, I use the above defined profile to check if the objectId exists in the claim before migration:
<!-- SIGN-IN -->
<TechnicalProfile Id="SelfAsserted-LocalAccountSignin-Email">
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="needToMigrate" />
</OutputClaims>
<ValidationTechnicalProfiles>
<!--First check if user exists in AD-->
<ValidationTechnicalProfile ReferenceId="AAD-UserCheckUsingEmailAddress" />
<!--Demo: Add user migration validation technical profile before login-NonInteractive.
Only execute migration if user does not exist in AD-->
<ValidationTechnicalProfile ReferenceId="REST-UserMigration-LocalAccount-SignIn" ContinueOnError="false" >
<Preconditions>
<Precondition Type="ClaimsExist" ExecuteActionsIf="true">
<Value>objectId</Value>
<Action>SkipThisValidationTechnicalProfile</Action>
</Precondition>
</Preconditions>
</ValidationTechnicalProfile>

Answer 1

Change this
<InputClaim ClaimTypeReferenceId="signInName" PartnerClaimType="username" Required="true" />
To
<InputClaim ClaimTypeReferenceId="signInName" PartnerClaimType="signInNames.emailAddress" Required="true" />
And this
<Item Key="RaiseErrorIfClaimsPrincipalDoesNotExist">true</Item>
To
<Item Key="RaiseErrorIfClaimsPrincipalDoesNotExist">false</Item>
This assumes that the user enters their email into a textbox (or otherwise acquired) with claim name signInName, and the users identifier is stored in signInNames.emailAddress.
https://learn.microsoft.com/en-us/azure/active-directory-b2c/active-directory-technical-profile#inputclaims
PartnerClaimType username Is not valid. There is no attribute on the user called username.
This sample does something similar
https://github.com/azure-ad-b2c/user-migration/tree/master/seamless-account-migration
https://github.com/azure-ad-b2c/user-migration/blob/master/seamless-account-migration/policy/TrustFrameworkExtensionsSeamlessMigration.xml#L52