Automated Heroku account signup using App Engine
Register a new App Engine application, edit application field of app.yaml, then deploy to App Engine. You can now create a Heroku account by POSTing to:
https://<appname>.appspot.com/new
username=<desired user identifier>
password=<desired password>
This will kick off the signup process. If started successfully, it will return 201 Created with a Location header. This doesn't mean the account is ready to use. It's going to generate an email address that looks like this:
<username>@<appname>.appspotmail.com
This email address will be "invited" to Heroku by a link sent to it. Our service receives this email and parses it to finish the signup process.
After the above request, you need to poll the URL in the Location header until it returns 200 with full account credentials before you can login with this account. The URL in the Location header looks like this:
https://<appname>.appspot.com/new/<username>@<appname>.appspotmail.com
Perform a GET request that follows redirects. Very likely, account creation will be done and you'll receive JSON that looks like this:
{"email": "<username>@<appname>.appspotmail.com", "password": "<password>"}
This means you can now login with those credentials. If the invitation email has not been received and the account is still not ready, the request will wait up to 25 seconds. If by then the account is not ready, it will return a 307 redirect to itself and try again, effectively giving you long-polling.
If there was an error with creation on Heroku, you'll receive a 503 with the details in the body. If the account was not created for any other reason, after 5 minutes the request expires and you'll receive a 404.