Allow applications to require a High Security token without doing a session upgrade
In some cases (like managing your email addresses) it makes sense to upgrade your session for a little while since it's common to make multiple edits in sequence (add a new address, make it primary, remove an old address). We generally want MFA to stay out of the way and not feel annoying.
In other cases, we don't expect multiple high-security actions in a row. Notably, PHI873 looks at more "one-shot" use cases where a prompt is answering a specific workflow. We already have at least one of these in the upstream: answering an MFA prompt when signing a Legalpad document.
Introduce a "token" workflow (in contrast to the existing "session") workflow that just does a one-shot prompt without upgrading your session statefully. Then, make Legalpad use this new workflow.
Note that this workflow has a significant problem: if the form submission is invalid for some other reason, we re-prompt you on resubmit. In Legalpad, this workflow looks like:
- Forget to check the "I agree" checkbox.
- Submit the form.
- Get prompted for MFA.
- Answer MFA prompt.
- Get dumped back to the form with an error.
- When you fix the error and submit again, you have to do another MFA check.
This isn't a fatal flaw in Legalpad, but would become a problem with wider adoption. I'll work on fixing this (so the MFA token sticks to the form) in the next set of changes.
Roughly, this is headed toward "MFA sticks to the form/workflow" instead of "MFA sticks to the user/session".
- Signed a legalpad document with MFA enabled.
- Was prompted for MFA.
- Session no longer upgraded (no purple "session in high security" badge).
- Submitted form with error, answered MFA, fixed error, submitted form again.
- Bad behavior: got re-prompted for MFA. In the future, MFA should stick to the form.
Reviewed By: amckinley
Maniphest Tasks: T13222
Differential Revision: https://secure.phabricator.com/D19843