A relevant question was published in 2016 (https://stackoverflow.com/questions/37079547/cloudflare-origin-certificate-with-google-app-engine).
The cloudflare documentation is dated April 2019 (https://support.cloudflare.com/hc/en-us/articles/115000479507). It says
but it is difficult to say whether this section has been reviewed recently.
I am not sure if the situation has changed since.
I decided to try it. Here is the screen capture of the Google App Engine interface:
I have downloaded the certificate of origin and the private key. I have downloaded the cert. And then convert the key by running
openssl rsa -in priv_key.pem -out priv_key.rsa.pem
When I clicked on upload, I had the following error:
I'm pretty sure they're the same since I just downloaded them a few minutes ago.
My questions are:
1) Can GAE accept the Cloudflare Certificate of Origin?
2) Have I forgotten a step when I prepare the certificate of origin for GAE?