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Security21 December 2020·3 min read

How do magic links work and why should you use them?

Security work is mostly the business of removing footguns before someone finds them.

Paycux engineering

Security work is mostly the business of removing footguns before someone finds them. The interesting question is rarely whether an attack is possible — it is whether the ordinary path through your system makes it easy.

This piece walks through how we think about it at Paycux, what we have changed our minds about, and where the sharp edges are.

What are magic links?

That brings us to what are magic links?. Detection beats prevention when prevention is uncertain. If you cannot stop a class of abuse outright, make sure it produces a signal loud enough that someone sees it the same day.

Rotate on a schedule, not on an incident. A rotation path that has been exercised is a routine change; one that has never been used is an outage waiting for the worst possible moment.

How magic links work

Consider how magic links work. Rotate on a schedule, not on an incident. A rotation path that has been exercised is a routine change; one that has never been used is an outage waiting for the worst possible moment.

Blast radius is the metric that actually matters. A credential that can read one organization's data is an incident; the same credential scoped to every organization is a company-ending event, and the difference is a design decision made months earlier.

  • Scope credentials to the smallest useful blast radius
  • Alert on the abuse you cannot prevent
  • Exercise the rotation path before you need it
  • Log the decision, not just the outcome

The security implications of magic links

The security implications of magic links deserves its own treatment. Rotate on a schedule, not on an incident. A rotation path that has been exercised is a routine change; one that has never been used is an outage waiting for the worst possible moment.

Blast radius is the metric that actually matters. A credential that can read one organization's data is an incident; the same credential scoped to every organization is a company-ending event, and the difference is a design decision made months earlier.

Rotate on a schedule, not on an incident.

Magic links and user experience

Magic links and user experience deserves its own treatment. Detection beats prevention when prevention is uncertain. If you cannot stop a class of abuse outright, make sure it produces a signal loud enough that someone sees it the same day.

Blast radius is the metric that actually matters. A credential that can read one organization's data is an incident; the same credential scoped to every organization is a company-ending event, and the difference is a design decision made months earlier.

An alternative to magic links

An alternative to magic links is where this gets concrete. Rotate on a schedule, not on an incident. A rotation path that has been exercised is a routine change; one that has never been used is an outage waiting for the worst possible moment.

Detection beats prevention when prevention is uncertain. If you cannot stop a class of abuse outright, make sure it produces a signal loud enough that someone sees it the same day.

Where this leaves us

If there is one thing worth taking away, it is that the expensive decisions are the ones made implicitly. Making them on purpose costs an afternoon.

If you are working through the same problem and want to compare notes, the docs cover the mechanics and the console shows the behaviour on your own data.

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