4f63b99cee
Define my YNAB personal access token as an environment variable. Prefix Monzo environment variables with "monzo_" to more easily differentiate between Monzo credentials and YNAB credentials.
125 lines
4 KiB
Go
125 lines
4 KiB
Go
// Exporting Monzo transactions to my YouNeedABudget.com (i.e. YNAB)
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// account. YNAB unfortunately doesn't currently offer an Monzo integration. As
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// a workaround and a practical excuse to learn Go, I decided to write one
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// myself.
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//
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// This job is going to run N times per 24 hours. Monzo offers webhooks for
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// reacting to certain types of events. I don't expect I'll need realtime data
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// for my YNAB integration. That may change, however, so it's worth noting.
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package main
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import (
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"encoding/json"
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"fmt"
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"log"
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"net/http"
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"net/url"
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"os"
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"os/exec"
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)
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////////////////////////////////////////////////////////////////////////////////
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// Constants
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////////////////////////////////////////////////////////////////////////////////
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var (
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clientId = os.Getenv("monzo_client_id")
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clientSecret = os.Getenv("monzo_client_secret")
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)
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const (
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redirectURI = "http://localhost:8080/authorization-code"
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// TODO(wpcarro): Consider generating a random string for the state when the
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// application starts instead of hardcoding it here.
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state = "xyz123"
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)
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////////////////////////////////////////////////////////////////////////////////
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// Business Logic
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////////////////////////////////////////////////////////////////////////////////
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// This is the response returned from Monzo when we exchange our authorization
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// code for an access token. While Monzo returns additional fields, I'm only
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// interested in AccessToken and RefreshToken.
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type accessTokenResponse struct {
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AccessToken string `json:"access_token"`
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RefreshToken string `json:"refresh_token"`
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}
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// TODO(wpcarro): Replace http.PostForm and other similar calls with
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// client.postForm. The default http.Get and other methods doesn't timeout, so
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// it's better to create a configured client with a value for the timeout.
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func getAccessToken(code string) {
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res, err := http.PostForm("https://api.monzo.com/oauth2/token", url.Values{
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"grant_type": {"authorization_code"},
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"client_id": {clientId},
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"client_secret": {clientSecret},
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"redirect_uri": {redirectURI},
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"code": {code},
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})
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failOn(err)
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defer res.Body.Close()
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payload := accessTokenResponse{}
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json.NewDecoder(res.Body).Decode(&payload)
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log.Printf("Access token: %s\n", payload.AccessToken)
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log.Printf("Refresh token: %s\n", payload.AccessToken)
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}
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func listenHttp(sigint chan os.Signal) {
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// Use a go-routine to listen for interrupt signals to shutdown our HTTP
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// server.
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go func() {
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<-sigint
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// TODO(wpcarro): Do we need context here? I took this example from the
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// example on golang.org.
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log.Println("Warning: I should be shutting down and closing the connection here, but I'm not.")
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close(sigint)
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}()
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log.Fatal(http.ListenAndServe(":8080", http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
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// 1. Get authorization code from Monzo.
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if req.URL.Path == "/authorization-code" {
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params := req.URL.Query()
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reqState := params["state"][0]
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code := params["code"][0]
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if reqState != state {
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log.Fatalf("Value for state returned by Monzo does not equal our state. %s != %s", reqState, state)
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}
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// TODO(wpcarro): Add a more interesting authorization confirmation
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// screen -- or even nothing at all.
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fmt.Fprintf(w, "Authorized!")
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// Exchange the authorization code for an access token.
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getAccessToken(code)
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return
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}
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log.Printf("Unhandled request: %v\n", *req)
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})))
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}
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// Open a web browser to allow the user to authorize this application.
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// TODO(wpcarro): Prefer using an environment variable for the web browser
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// instead of assuming it will be google-chrome.
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func authorizeClient() {
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url := fmt.Sprintf("https://auth.monzo.com/?client_id=%s&redirect_uri=%s&response_type=code&state=%s", clientId, redirectURI, state)
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exec.Command("google-chrome", url).Start()
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}
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func main() {
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sigint := make(chan os.Signal, 1)
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// TODO(wpcarro): Remove state here. I'm using as a hack to prevent my
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// program from halting before I'd like it to. Once I'm more comfortable
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// using channels, this should be a trivial change.
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state := make(chan bool)
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authorizeClient()
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listenHttp(sigint)
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<-state
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}
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