authhandler: Add authCodeOpts param to TokenSource

Certain implementations of OAuth2 (such as Reddit) have extra parameters
available as part of their OAuth2 flow. This commit adds the variadic
parameter `authCodeOpts` to the TokenSource function in authhandler,
allowing a caller to pass as many of these extra URL parameters as they
want or need.

Tests in the authhandler package have also been updated to reflect this
change.

**Does this commit introduce any breaking changes?**

No. The new parameter is variadic, as are its uses, which means that
existing code will not be affected by this change.

authhandler/authhandler.go

@@ -32,19 +32,25 @@ type AuthorizationHandler func(authCodeURL string) (code string, state string, e
 // This token source will verify that the "state" is identical in the request
 // and response before exchanging the auth code for OAuth token to prevent CSRF
 // attacks.
-func TokenSource(ctx context.Context, config *oauth2.Config, state string, authHandler AuthorizationHandler) oauth2.TokenSource {
-	return oauth2.ReuseTokenSource(nil, authHandlerSource{config: config, ctx: ctx, authHandler: authHandler, state: state})
+func TokenSource(ctx context.Context, config *oauth2.Config,
+	state string, authHandler AuthorizationHandler, authCodeOpts ...oauth2.AuthCodeOption) oauth2.TokenSource {
+
+	return oauth2.ReuseTokenSource(
+		nil,
+		authHandlerSource{config: config, ctx: ctx, authHandler: authHandler, state: state, opts: authCodeOpts},
+	)
 }
 
 type authHandlerSource struct {
 	ctx         context.Context
 	config      *oauth2.Config
 	authHandler AuthorizationHandler
 	state       string
+	opts        []oauth2.AuthCodeOption
 }
 
 func (source authHandlerSource) Token() (*oauth2.Token, error) {
-	url := source.config.AuthCodeURL(source.state)
+	url := source.config.AuthCodeURL(source.state, source.opts...)
 	code, state, err := source.authHandler(url)
 	if err != nil {
 		return nil, err

authhandler/authhandler_test.go

@@ -15,22 +15,17 @@ import (
 )
 
 func TestTokenExchange_Success(t *testing.T) {
-	authhandler := func(authCodeURL string) (string, string, error) {
-		if authCodeURL == "testAuthCodeURL?client_id=testClientID&response_type=code&scope=pubsub&state=testState" {
-			return "testCode", "testState", nil
-		}
-		return "", "", fmt.Errorf("invalid authCodeURL: %q", authCodeURL)
-	}
-
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		r.ParseForm()
 		if r.Form.Get("code") == "testCode" {
 			w.Header().Set("Content-Type", "application/json")
+
 			w.Write([]byte(`{
 				"access_token": "90d64460d14870c08c81352a05dedd3465940a7c",
 				"scope": "pubsub",
 				"token_type": "bearer",
-				"expires_in": 3600
+				"expires_in": 3600,
+				"duration": "permanent"
 			}`))
 		}
 	}))
@@ -45,26 +40,59 @@ func TestTokenExchange_Success(t *testing.T) {
 		},
 	}
 
-	tok, err := TokenSource(context.Background(), conf, "testState", authhandler).Token()
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !tok.Valid() {
-		t.Errorf("got invalid token: %v", tok)
-	}
-	if got, want := tok.AccessToken, "90d64460d14870c08c81352a05dedd3465940a7c"; got != want {
-		t.Errorf("access token = %q; want %q", got, want)
-	}
-	if got, want := tok.TokenType, "bearer"; got != want {
-		t.Errorf("token type = %q; want %q", got, want)
-	}
-	if got := tok.Expiry.IsZero(); got {
-		t.Errorf("token expiry is zero = %v, want false", got)
-	}
-	scope := tok.Extra("scope")
-	if got, want := scope, "pubsub"; got != want {
-		t.Errorf("scope = %q; want %q", got, want)
+	testExchange := func(authHandler AuthorizationHandler, opts ...oauth2.AuthCodeOption) {
+		tok, err := TokenSource(context.Background(), conf, "testState", authHandler, opts...).Token()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !tok.Valid() {
+			t.Errorf("got invalid token: %v", tok)
+		}
+		if got, want := tok.AccessToken, "90d64460d14870c08c81352a05dedd3465940a7c"; got != want {
+			t.Errorf("access token = %q; want %q", got, want)
+		}
+		if got, want := tok.TokenType, "bearer"; got != want {
+			t.Errorf("token type = %q; want %q", got, want)
+		}
+		if got := tok.Expiry.IsZero(); got {
+			t.Errorf("token expiry is zero = %v, want false", got)
+		}
+		scope := tok.Extra("scope")
+		if got, want := scope, "pubsub"; got != want {
+			t.Errorf("scope = %q; want %q", got, want)
+		}
+
+		if opts != nil && len(opts) > 0 {
+			duration := tok.Extra("duration")
+			if got, want := duration, "permanent"; got != want {
+				t.Errorf("duration = %q; want %q", got, want)
+			}
+		}
 	}
+
+	t.Run("test no extra options", func(t *testing.T) {
+		authhandler := func(authCodeURL string) (string, string, error) {
+			if authCodeURL == "testAuthCodeURL?client_id=testClientID&response_type=code&scope=pubsub&state=testState" {
+				return "testCode", "testState", nil
+			}
+			return "", "", fmt.Errorf("invalid authCodeURL: %q", authCodeURL)
+		}
+
+		testExchange(authhandler)
+	})
+
+	t.Run("test with AuthCodeOptions", func(t *testing.T) {
+		authhandler := func(authCodeURL string) (string, string, error) {
+			if authCodeURL == "testAuthCodeURL?client_id=testClientID&duration=permanent&response_type=code&scope=pubsub&state=testState" {
+				return "testCode", "testState", nil
+			}
+			return "", "", fmt.Errorf("invalid authCodeURL: %q", authCodeURL)
+		}
+
+		testAuthOpt := oauth2.SetAuthURLParam("duration", "permanent")
+
+		testExchange(authhandler, testAuthOpt)
+	})
 }
 
 func TestTokenExchange_StateMismatch(t *testing.T) {