Based on the Social and Local with MFA starter pack, implemants Conditional Access-based rules for user blocking or requiring MFA or password change. the policy will return an OAuth2 eror to the application. Please uncomment/comment lines 491/492 to display a blocking page instead.

Use IefPolicies module with the following command

Add-IefPoliciesSample ConditionalAccess -owner mrochon -repo b2csamples

to add to an existing SocialLocal with MFA policy set

elements of this extensions were copied from the B2C Community sample