* Remove authentication, including SessionAuthentication, to fix CSRF
exemption by dropping CSRF check of SessionAuthentication.
* Several changes to make it more clear that only POST is supported and
clean up GET method testing.
* Removed the temporary 403 error logging that wasn't working.
* Removed test_single_access_token which was written for DOP, but
doesn't work with DOT. See
[MA-2122](https://openedx.atlassian.net/browse/MA-2122) for a ticket
about implementing this for DOT, although it doesn't seem to be a
priority. NOTE: A comment was added to the ticket explaining that this
test was removed.
* GET now returns default error for methods not allowed.
ARCHBOM-1667
40611bb915