title: Look up user in AAD based on AADB2C attribute value
body: <p>If I have a user in Aure AD B2C that was created based on an Azure AD (enterprise) identity (as described here: <a href="https://docs.microsoft.com/en-us/azure/active-directory-b2c/active-directory-b2c-setup-aad-custom" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/active-directory-b2c/active-directory-b2c-setup-aad-custom</a>), is there an attribute stored in AADB2C that will allow me to look up (using Graph API or similar) the user object in AAD?  I see that among the AADB2C attributes there is  <strong>userPrincipalName</strong> and <strong>issuerUserId</strong> but it's not obvious to me if either of these match any value stored in AAD.</p>
  
  <p>thanks!</p>
  
  <p>Martin</p>