Hello @Syed Mustafa Shah Please find my comments inline:
1- How can we customize our existing login policy (build in user flow) for sign in to identify old users and redirect them to Auth app signup screen.
In order to identify whether the user is new or old, you can configure the user flow with "User is new" Application Claim, which is returned as "newUser": true
claim in the token, if the user has just signed-up for your application. For subsequent sign-ins by that user, this claim will not be returned. As of now built-in user flows support Azure MFA with text message based 2nd factor only. Here is an active feedback link for adding Authenticator support with B2C user flows.
2- How can we implement a custom policy for invitation based sign up that will take the user to Auth app registration screen after creating a password.
Here is a sample for SignUp with email invitation, that you can configure to redirect the users to the policy configured with MFA totp.
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