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Blacklist user domains



Is it possible to create a blacklist of user domains to prevent sign-ups?


You can fail an authentication transaction in a custom rule (see an example of a whitelist based rule here). Technically this does not prevent the signup (user is still created), but it’s something that would be available across all types of authentication types (aka connection) and would have a similar effect to actually prevent the signup as the user (despite being created) will not be able to complete any authentication nor access your application.

If the scope of this restriction is narrower in terms of types of connections where you need to apply it then there may be more suitable options. For example, for database connections you could consider using the pre-registration hook to actually prevent the signup of the user if it fails a certain criteria.