          except self.model.DoesNotExist:
              raise exceptions.AuthenticationFailed(_("Invalid token"))
  
          if not token.user.is_active:
              raise exceptions.AuthenticationFailed(_("User inactive or deleted"))
  
          return (token.user, token)
  
      def authenticate_header(self, request):
          return 'Token'
 
</s> remove             raise exceptions.AuthenticationFailed(_("Invalid token"))
 </s> add             raise exceptions.AuthenticationFailed(_('Invalid token.')) </s> remove             raise exceptions.AuthenticationFailed(_("Invalid username/password."))
 </s> add             raise exceptions.AuthenticationFailed(_('Invalid username/password.')) </s> remove             msg = _("Invalid basic header. Credentials not correctly base64 encoded.")
 </s> add             msg = _('Invalid basic header. Credentials not correctly base64 encoded.') </s> remove             msg = _("Invalid basic header. No credentials provided.")
 </s> add             msg = _('Invalid basic header. No credentials provided.') </s> remove             msg = _("Invalid token header. No credentials provided.")
 </s> add             msg = _('Invalid token header. No credentials provided.')
            raise exceptions.AuthenticationFailed(_('User inactive or deleted.'))
          except self.model.DoesNotExist:
              raise exceptions.AuthenticationFailed(_("Invalid token"))
  
          if not token.user.is_active:
            raise exceptions.AuthenticationFailed(_('User inactive or deleted.'))
  
          return (token.user, token)
  
      def authenticate_header(self, request):
          return 'Token'
keep keep keep keep replace keep keep keep keep keep
 prefer single quotes in source and double quotes in user visible strings; add some missing full stops to user visible strings 
rest_framework/authentication.py