How to read user by claim in AAD B2C custom policy? - azure-ad-b2c

Question

Is there any option to read azure AD B2C tenant users (local or social) by a claim value such as email address or by custom claim such as extension_company_user_id etc.
Actually I need something like below:
<TechnicalProfile Id="AAD-UserReadUsingClaimValue">
<Metadata>
<Item Key="Operation">Read</Item>
</Metadata>
<IncludeInSso>false</IncludeInSso>
<InputClaims>
<InputClaim ClaimTypeReferenceId="company_user_id" PartnerClaimType="extenstion_company_user_id" />
</InputClaims>
<OutputClaims>
<!-- Required claims -->
<OutputClaim ClaimTypeReferenceId="objectId" />
<OutputClaim ClaimTypeReferenceId="authenticationSource" DefaultValue="localAccountAuthentication" />
<!-- Optional claims -->
<OutputClaim ClaimTypeReferenceId="country" />
<OutputClaim ClaimTypeReferenceId="userPrincipalName" />
<OutputClaim ClaimTypeReferenceId="otherMails" />
<OutputClaim ClaimTypeReferenceId="signInNames.emailAddress" />
<OutputClaim ClaimTypeReferenceId="extension_company_user_id" />
</OutputClaims>
<IncludeTechnicalProfile ReferenceId="AAD-Common" />
</TechnicalProfile>

Answer 1

You cannot do that because the claim has no uniqueness constraint. You need to read users by the signInNames property or the userIdentities/alternativeSecurityId property, these have a uniqueness constraint.
This would be valid:
<InputClaim ClaimTypeReferenceId="userEnteredEmail" PartnerClaimType="signInNames.emailAddress" />
If extenstion_company_user_id is going to be unique, and a user identifier, write it to signInNames.companyUserId. AAD B2C will automatically register the schema extension when doing so in custom policy.
Then you can read a user like this:
<InputClaim ClaimTypeReferenceId="company_user_id" PartnerClaimType="signInNames.companyUserId" />