In D25935#25149, @Cigaryno wrote:

Why would a cancel URI be needed?

In D25935#25135, @aklapper wrote:

After these steps I get Unhandled Exception ("Exception"): This transaction group requires MFA to apply, but the Editor was not configured with a Cancel URI. This workflow can not perform an MFA check.

Why would a cancel URI be needed? Do you know a Cancel URI for an app with something that prompts for MFA (ie. exposing Passphrases, empowering users, signing comments with MFA, managing your VCS password and SSH keys)

In D25935#25144, @Cigaryno wrote:

In D25935#25135, @aklapper wrote:

Which "an application" exactly?

Any application were canUninstall is not set to false (thus not a required application).

That's what I tested (as the Files application can be uninstalled). Which exact application(s) did you test?
I'm surprised that you did not run into the same problem as I did described in my last comment...maybe it's related to not being an admin?

In D25935#25135, @aklapper wrote:

Which "an application" exactly?

Any application were canUninstall is not set to false (thus not a required application).

As which type of user?

A user with the Can Configure Application capability (by default admins).

Clear Test Plans with URIs are welcome - the less others need to think "how/where to do that" the easier gets testing.

I don't know if what I done on D25935 is correct, but as usual, Request Changes if I did it wrong.
I relied on the code on PhabricatorUserEmpowerTransaction to try to make PhabricatorApplicationUninstallTransaction require MFA if enabled.

Make lint happy