Support for Installed Applications Flow

I didn't find any information about support for installed applications which use redirect_uri=urn:ietf:wg:oauth:2.0:oob.
This currently leads to a redirectal error, which is perfectly correct, but shall lead to a page containing the access_token inside the html body response.

Thanks for your support.

No files or tests are named. Start by locating the authorization endpoint handling redirect_uri=urn:ietf:wg:oauth:2.0:oob, then verify that the installed-application flow returns an HTML body containing the access_token instead of a redirect error. Add coverage for the expected response.

Written by the indexing model from the issue text.