Make it easy to satisfy the Let's Encrypt challenge without changing code.
Review Request #8571 — Created Dec. 14, 2016 and submitted
Because Heroku doesn't have built-in support for Let's Encrypt, we need to
generate (and renew) the certificate in manual mode. This requires setting up a
special endpoint on the server to serve a secret so that they can verify that
we actually do own the domain that the certificate is being issued for.So far I've done this by pushing a special build, but that's kind of icky. This
change makes it possible to do the challenge/response by changing environment
variables in the application config.
Used this while renewing the SSL certificate.