AuthFailure.swift

func refreshAuth(_ username: String, _ password: String) -> Request {
    return self.login(username, password, onSuccess: {
        }, onFailure: { error in
    })
}

func refreshTokenOnAuthFailure(request: Siesta.Request) -> Request {
    return request.chained {
        guard case .failure(let error) = $0.response,  // Did request fail…
            error.httpStatusCode == 401 else {           // …because of expired token?
                return .useThisResponse                    // If not, use the response we got.
        }

        return .passTo(
            self.refreshAuth("test", "test").chained {             // If so, first request a new token, then:
                if case .failure = $0.response {           // If token request failed…
                    return .useThisResponse                  // …report that error.
                } else {
                    return .passTo(request.repeated())       // We have a new token! Repeat the original request.
                }
            }
        )
    }
}