ValueError when using Basic Auth with malformed credentials

[poswald]

A request to authenticate with malformed credentials causes a server error rather than a 4XX level error:

$ curl -X POST --data 'grant_type=client_credentials' -H 'Authorization: Basic asdf asdf'  http://localhost:8000/user/oauth2/token/

The problem comes from having too many spaces in the Authorization header which breaks _extract_basic_auth:

File "/Users/poswald/myproject/env/lib/python2.7/site-packages/oauth2_provider/oauth2_validators.py" in _extract_basic_auth
  37.         auth_type, auth_string = auth.split(' ')

Exception Type: ValueError at /user/oauth2/token/
Exception Value: too many values to unpack

[masci]

TODO: check this is fixed by #185

[masci]

Fixed with #185