Document how to allow only certain domain names from signing up

[aeneasr]

Preflight checklist

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Describe your problem

Using blocking web hooks ( https://github.com/ory/docs/pull/678/files ) one can create a web hook which returns an error if a user signs up that is not associated to a specific domain (e.g. mycompany.org).

Describe your ideal solution

We need to add a guide which explains how to set up "domain-based" allow-lists for sign up processes.

Workarounds or alternatives

None

Version

master

Additional Context

No response