Q1. What is the problem that you are trying to solve?
Currently 7.1 is not officially supported by passbolt.
The mcrypt extension is deprecated on PHP 7.1
Q2 - Who is impacted?
Q3 - Why is it important and/or urgent?
Security, reducing technological debt.
Q4 - What is your proposed solution? (optional)
Migrate to cakephp3 and fix travis 7.1 build.