Since 5.6, Laravel has shipped with functionality to sign URLs. These URLs append a "signature" to the query string, so that Laravel can verify that the link has not been tampered with since it was created. This also allows you to generate temporary signed routes that expire after a configured period of time.
This is useful for things like verifying account emails, or enabling passwordless logins.
Passwordless logins is something that is quite useful for an application, but what if you wanted to be able to generate a signed URL in one application that would allow you to log in to a second application?
He starts by defining the use case, requiring multiple signing keys to be used, one for customer URLs and another for admin URLs accessing the same content. He makes this work through the use of a custom key resolver, pulling the key for the signing dynamically. He also shows how to update the passthrough authentication handling, allowing the administrators (staff) of the system to bypass normal authentication handling and more directly view the user's information.