Move authorization logic into separate package

Relocated the logic for authorizing clients into a separate package that the
tokens server now depends on. Moving this helped me separate concerns. I removed
a few top-level variables and tried to write more pure versions of the
authorization functions to avoid leaking Monzo-specific details.

3 files changed, 115 insertions, 146 deletions

diff --git a/monzo_ynab/auth.go b/monzo_ynab/auth.go
new file mode 100644
index 000000000000..b66bacb10687
--- /dev/null
+++ b/monzo_ynab/auth.go
@@ -0,0 +1,101 @@
+package auth
+
+////////////////////////////////////////////////////////////////////////////////
+// Dependencies
+////////////////////////////////////////////////////////////////////////////////
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"os/exec"
+	"utils"
+)
+
+////////////////////////////////////////////////////////////////////////////////
+// Constants
+////////////////////////////////////////////////////////////////////////////////
+
+var (
+	BROWSER      = os.Getenv("BROWSER")
+	REDIRECT_URI = "http://localhost:8080/authorization-code"
+)
+
+////////////////////////////////////////////////////////////////////////////////
+// Types
+////////////////////////////////////////////////////////////////////////////////
+
+// This is the response returned from Monzo when we exchange our authorization
+// code for an access token. While Monzo returns additional fields, I'm only
+// interested in AccessToken and RefreshToken.
+type accessTokenResponse struct {
+	AccessToken  string `json:"access_token"`
+	RefreshToken string `json:"refresh_token"`
+	ExpiresIn    int    `json:"expires_in"`
+}
+
+type Tokens struct {
+	AccessToken  string
+	RefreshToken string
+	ExpiresIn    int
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Functions
+////////////////////////////////////////////////////////////////////////////////
+
+// Returns the access token and refresh tokens for the Monzo API.
+func GetTokensFromAuthCode(authCode string, clientID string, clientSecret string) *Tokens {
+	res, err := http.PostForm("https://api.monzo.com/oauth2/token", url.Values{
+		"grant_type":    {"authorization_code"},
+		"client_id":     {clientID},
+		"client_secret": {clientSecret},
+		"redirect_uri":  {REDIRECT_URI},
+		"code":          {authCode},
+	})
+	utils.FailOn(err)
+	defer res.Body.Close()
+	payload := &accessTokenResponse{}
+	json.NewDecoder(res.Body).Decode(payload)
+
+	return &Tokens{payload.AccessToken, payload.RefreshToken, payload.ExpiresIn}
+}
+
+// Open a web browser to allow the user to authorize this application. Return
+// the authorization code sent from Monzo.
+func GetAuthCode(clientID string) string {
+	// TODO(wpcarro): Consider generating a random string for the state when the
+	// application starts instead of hardcoding it here.
+	state := "xyz123"
+	url := fmt.Sprintf(
+		"https://auth.monzo.com/?client_id=%s&redirect_uri=%s&response_type=code&state=%s",
+		clientID, REDIRECT_URI, state)
+	exec.Command(BROWSER, url).Start()
+
+	authCode := make(chan string)
+	go func() {
+		log.Fatal(http.ListenAndServe(":8080",
+			http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+				// 1. Get authorization code from Monzo.
+				if req.URL.Path == "/authorization-code" {
+					params := req.URL.Query()
+					reqState := params["state"][0]
+					code := params["code"][0]
+
+					if reqState != state {
+						log.Fatalf("Value for state returned by Monzo does not equal our state. %s != %s", reqState, state)
+					}
+					authCode <- code
+
+					fmt.Fprintf(w, "Authorized!")
+				} else {
+					log.Printf("Unhandled request: %v\n", *req)
+				}
+			})))
+	}()
+	result := <-authCode
+	return result
+}
diff --git a/monzo_ynab/main.go b/monzo_ynab/main.go
index 10dc9f3effe5..835cfadcb7db 100644
--- a/monzo_ynab/main.go
+++ b/monzo_ynab/main.go
@@ -10,157 +10,13 @@
 package main
 
 import (
-	"bytes"
-	"encoding/json"
 	"fmt"
-	"log"
-	"net/http"
-	"net/http/httputil"
-	"net/url"
-	"strings"
-	"os"
-	"os/exec"
-	"utils"
-)
-
-////////////////////////////////////////////////////////////////////////////////
-// Constants
-////////////////////////////////////////////////////////////////////////////////
-
-var (
-	accountId    = os.Getenv("monzo_account_id")
-	clientId     = os.Getenv("monzo_client_id")
-	clientSecret = os.Getenv("monzo_client_secret")
-)
-
-const (
-	redirectURI = "http://localhost:8080/authorization-code"
-	// TODO(wpcarro): Consider generating a random string for the state when the
-	// application starts instead of hardcoding it here.
-	state = "xyz123"
 )
 
 ////////////////////////////////////////////////////////////////////////////////
 // Business Logic
 ////////////////////////////////////////////////////////////////////////////////
 
-// This is the response returned from Monzo when we exchange our authorization
-// code for an access token. While Monzo returns additional fields, I'm only
-// interested in AccessToken and RefreshToken.
-type accessTokenResponse struct {
-	AccessToken  string `json:"access_token"`
-	RefreshToken string `json:"refresh_token"`
-	ExpiresIn    int    `json:"expires_in"`
-}
-
-type setTokensRequest struct {
-	AccessToken  string `json:"access_token"`
-	RefreshToken string `json:"refresh_token"`
-	ExpiresIn    int    `json:"expires_in"`
-}
-
-type Tokens struct {
-	AccessToken  string `json:"access_token"`
-	RefreshToken string `json:"refresh_token"`
-	ExpiresIn    int    `json:"expires_in"`
-}
-
-// TODO(wpcarro): Replace http.PostForm and other similar calls with
-// client.postForm. The default http.Get and other methods doesn't timeout, so
-// it's better to create a configured client with a value for the timeout.
-
-// Returns the access token and refresh tokens for the Monzo API.
-func getTokens(code string) *Tokens {
-	res, err := http.PostForm("https://api.monzo.com/oauth2/token", url.Values{
-		"grant_type":    {"authorization_code"},
-		"client_id":     {clientId},
-		"client_secret": {clientSecret},
-		"redirect_uri":  {redirectURI},
-		"code":          {code},
-	})
-	utils.FailOn(err)
-	defer res.Body.Close()
-	payload := &accessTokenResponse{}
-	json.NewDecoder(res.Body).Decode(payload)
-
-	return &Tokens{payload.AccessToken, payload.RefreshToken, payload.ExpiresIn}
-}
-
-// TODO(wpcarro): Prefer using an environment variable for the web browser
-// instead of assuming it will be google-chrome.
-// Open a web browser to allow the user to authorize this application. Return
-// the authorization code sent from Monzo.
-func getAuthCode() string {
-	url := fmt.Sprintf("https://auth.monzo.com/?client_id=%s&redirect_uri=%s&response_type=code&state=%s", clientId, redirectURI, state)
-	exec.Command("google-chrome", url).Start()
-
-	authCode := make(chan string)
-	go func() {
-		log.Fatal(http.ListenAndServe(":8080", http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
-			// 1. Get authorization code from Monzo.
-			if req.URL.Path == "/authorization-code" {
-				params := req.URL.Query()
-				reqState := params["state"][0]
-				code := params["code"][0]
-
-				if reqState != state {
-					log.Fatalf("Value for state returned by Monzo does not equal our state. %s != %s", reqState, state)
-				}
-				authCode <- code
-
-				fmt.Fprintf(w, "Authorized!")
-			} else {
-				log.Printf("Unhandled request: %v\n", *req)
-			}
-		})))
-	}()
-	result := <-authCode
-	return result
-}
-
-// TODO(wpcarro): Move this logic out of here and into the tokens server.
-func authorize() {
-	authCode := getAuthCode()
-	tokens := getTokens(authCode)
-	client := &http.Client{}
-
-	payload, _ := json.Marshal(setTokensRequest{
-		tokens.AccessToken,
-		tokens.RefreshToken,
-		tokens.ExpiresIn})
-	log.Printf("Access token: %s\n", tokens.AccessToken)
-	log.Printf("Refresh token: %s\n", tokens.RefreshToken)
-	log.Printf("Expires: %s\n", tokens.ExpiresIn)
-	req, _ := http.NewRequest("POST", "http://localhost:4242/set-tokens", bytes.NewBuffer(payload))
-	req.Header.Set("Content-Type", "application/json")
-	_, err := client.Do(req)
-	utils.FailOn(err)
-}
-
-// Retrieves the access token from the tokens server.
-func getAccessToken() string {
-	return simpleGet("http://localhost:4242/token")
-}
-
 func main() {
-	accessToken := getAccessToken()
-	// authHeaders := map[string]string{
-	// 	"Authorization": fmt.Sprintf("Bearer %s", accessToken),
-	// }
-
-	client := &http.Client{}
-	form := url.Values{"account_id": {accountId}}
-	req, _ := http.NewRequest("GET", "https://api.monzo.com/transactions", strings.NewReader(form.Encode()))
-	req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", accessToken))
-	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
-	bytes, _ := httputil.DumpRequest(req, true)
-	fmt.Println(string(bytes))
-	res, _ := client.Do(req)
-	bytes, _ = httputil.DumpResponse(res, true)
-	fmt.Println(string(bytes))
-
-	// res := simpleGet("https://api.monzo.com/accounts", authHeaders, true)
-	// fmt.Println(res)
-
-	os.Exit(0)
+	fmt.Println("To be implemented...")
 }
diff --git a/monzo_ynab/tokens.nix b/monzo_ynab/tokens.nix
index 6b932e3975ad..a00191a20782 100644
--- a/monzo_ynab/tokens.nix
+++ b/monzo_ynab/tokens.nix
@@ -4,12 +4,24 @@
   ...
 }:
 
-depot.buildGo.program {
+let
+  auth = depot.buildGo.package {
+    name = "auth";
+    srcs = [
+      ./auth.go
+    ];
+    deps = with briefcase.gopkgs; [
+      utils
+    ];
+  };
+in depot.buildGo.program {
   name = "token-server";
   srcs = [
     ./tokens.go
   ];
   deps = with briefcase.gopkgs; [
     kv
+    utils
+    auth
   ];
 }