I'm creating a custom policy in Azure AD B2C to let invited users sign in via another Azure AD (or even ADFS). The problem I have is that a new user gets created when they sign in (rather than the invited user). I have found that I have been trying to find existing user in my AAD using alternativesecurityid or objectid and both of these are not matching. So I think I need to find an existing user by email, and not any IDs. This too, is not working, because I can see my invited user's email is sitting in otherMails and mail properties (via GraphAPI), and apparently I cannot query B2C via these fields.
<TechnicalProfile Id="AAD-ReadUserByEmail">
<Metadata>
<Item Key="Operation">Read</Item>
<Item Key="RaiseErrorIfClaimsPrincipalDoesNotExist">false</Item>
</Metadata>
<InputClaims>
<InputClaim ClaimTypeReferenceId="emailFromSocialAccount" PartnerClaimType="mail" Required="true" />
</InputClaims>
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="objectId" />
<OutputClaim ClaimTypeReferenceId="displayName" />
<OutputClaim ClaimTypeReferenceId="givenName" />
<OutputClaim ClaimTypeReferenceId="surname" />
<OutputClaim ClaimTypeReferenceId="userPrincipalName" />
</OutputClaims>
<IncludeTechnicalProfile ReferenceId="AAD-Common" />
</TechnicalProfile>
Only <InputClaim ClaimTypeReferenceId="emailFromSocialAccount" PartnerClaimType="signInNames.emailAddress" Required="true" />
passes validation, but this field is not having any data.
How do I find the invited user?