def GenerateClientLoginAuthToken(http_body):
  """Returns the token value to use in Authorization headers.

  Reads the token from the server's response to a Client Login request and
  creates header value to use in requests.

  Args:
    http_body: str The body of the server's HTTP response to a Client Login
        request
 
  Returns:
    The value half of an Authorization header.
  """
  for response_line in http_body.splitlines():
    if response_line.startswith('Auth='):
      # Strip off the leading Auth= and return the Authorization value.
      return 'GoogleLogin auth=%s' % response_line[5:]
  return None