If the "given_name" doesn't came in the token an error occurs after signup

[davidjrh]

When signin up, if the administrator hasn't setup the "given_name" and "surname" as mandatory, the user can register without specifying and leaving it blank. Azure AD B2C allow this (only e-mail is required), so when the user is redirected to the DNN site, an exception is thrown because the current codebase checks for that claim when creating the local user.

Since Azure AD B2C allows this user creation, the idea is to use the given name "Unknown" in the same way it's shown on the Azure portal.

PS: to setup the mandatory field you need to customize the signup policy being used (see https://stackoverflow.com/questions/47738301/azure-b2c-signup-policy-with-mandatory-fields)