There should be only one blank line here.

You can put the """ on the same line when the docstring is just one line.

Remove this line.

Single-line if statements in python don't need parens. It's also somewhat more idiomatic to write if not request.user.is_authenticated():

Can you put a comma after this?

Can you put a comma after this?

Trailing whitespace.

Imports should be in alphabetical order (within their pep-8 defined section)

There's a few problems with this line. First of all, I don't know what this comment means. Second, there should be a space after the #. Third, comments should be full sentences with capitalization, and last, there's some trailing whitespace.

This is a review from Review Bot.
  Tool: PEP8 Style Checker
  Processed Files:
    reviewboard/webapi/resources/session.py
    reviewboard/webapi/tests/test_session.py
  Ignored Files:

Col: 27
 E203 whitespace before ':'

Col: 1
 W293 blank line contains whitespace

Col: 13
 E128 continuation line under-indented for visual indent

Col: 34
 W291 trailing whitespace

Col: 1
 W391 blank line at end of file

This is a review from Review Bot.
  Tool: Pyflakes
  Processed Files:
    reviewboard/webapi/resources/session.py
    reviewboard/webapi/tests/test_session.py
  Ignored Files:

 'User' imported but unused

 'Session' imported but unused

 'get_session_url' imported but unused

 'SessionStore' imported but unused

 'Session' imported but unused

I'm going to make some changes to this and push it. Thanks!