A MITM TLS-busting proxy. Like on many corporate networks and in many country firewalls. Might seem like a remote chance from a user's point of view, but could

A MITM TLS-busting proxy. Like on many corporate networks and in many country firewalls. Might seem like a remote chance from a user's point of view, but could be a threat from a payment processor's view, with billions of daily transactions. Also, easier to prove the integrity of the message when you're handling the authentication piece yourself rather than assuming TLS was correctly enforced end-to-end.