For applications without a web sever ("native apps" in the Canvas doc), you can use urn:ietf:wg:oauth:2.0:oob as the redirect_url.. The redirect then goes to a page on the Canvas server with a URL like:

   .../login/oauth2/auth?code=047f524c6b1d8bd6522670....

The user can then copy the code and insert it into your non-server application.  The application can then get the token.

The main issue is having clear instructions to the end user about getting the code from the URL and putting it into your application.  It would be nice if Canvas would put the code on the actual web page with some sort of instructions.

BTW, for testing its easy to fire up a slightly old, but adequate, AWS AMI, or more recent versions at Bitnami.