wsgi: Subclass Unauthorized when dealing with SSL authentication error.

Allows introducing more reasons to reject authentication, with different
WWW-Authenticate values.

caucase/wsgi.py

@@ -53,6 +53,11 @@ class Unauthorized(ApplicationError):
   HTTP unauthorized error
   """
   status = _getStatus(httplib.UNAUTHORIZED)
+
+class SSLUnauthorized(Unauthorized):
+  """
+  Authentication failed because of SSL credentials (missing or incorrect)
+  """
   _response_headers = [
     # XXX: non standard scheme, suggested in
     # https://www.ietf.org/mail-archive/web/httpbisa/current/msg03764.html
@@ -250,7 +255,7 @@ class Application(object):
         ),
       )
     except (exceptions.CertificateVerificationError, ValueError):
-      raise Unauthorized
+      raise SSLUnauthorized
     header_list.append(('Cache-Control', 'private'))
 
   def _readJSON(self, environ):