I figured it out.
Git's inline help, upon not knowing who you are, makes the suggestions:
git config --global user.email <email>
git config --global user.name <name>
Cloudron's problem is "--global". It has no problem with setting the user.name and user.email for a particular /app.
So this solved my problem:
git config user.email <email>
git config user.name <name>
of course substituting my email address for "<email>" and my name for "<name>".