authhandler: Add support for PKCE
- Added new TokenSourceWithPKCE function to authhandler package.
- Updated Token method to support PKCE flow, sending code challenge and challenge method on the auth-code request, and sending code verifier on the exchange request.
- Updated google/default.go to support PKCE param.
Change-Id: Iab895bc01407c4742706061753f5329a772068ec
GitHub-Last-Rev: c1fddd28bcc4c7bd265573111808427711d7ba37
GitHub-Pull-Request: golang/oauth2#568
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/410515
Run-TryBot: Cody Oss <codyoss@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Shin Fan <shinfan@google.com>
Reviewed-by: Cody Oss <codyoss@google.com>
diff --git a/authhandler/authhandler.go b/authhandler/authhandler.go
index 69967cf..9bc6cd7 100644
--- a/authhandler/authhandler.go
+++ b/authhandler/authhandler.go
@@ -13,11 +13,36 @@
"golang.org/x/oauth2"
)
+const (
+ // Parameter keys for AuthCodeURL method to support PKCE.
+ codeChallengeKey = "code_challenge"
+ codeChallengeMethodKey = "code_challenge_method"
+
+ // Parameter key for Exchange method to support PKCE.
+ codeVerifierKey = "code_verifier"
+)
+
+// PKCEParams holds parameters to support PKCE.
+type PKCEParams struct {
+ Challenge string // The unpadded, base64-url-encoded string of the encrypted code verifier.
+ ChallengeMethod string // The encryption method (ex. S256).
+ Verifier string // The original, non-encrypted secret.
+}
+
// AuthorizationHandler is a 3-legged-OAuth helper that prompts
// the user for OAuth consent at the specified auth code URL
// and returns an auth code and state upon approval.
type AuthorizationHandler func(authCodeURL string) (code string, state string, err error)
+// TokenSourceWithPKCE is an enhanced version of TokenSource with PKCE support.
+//
+// The pkce parameter supports PKCE flow, which uses code challenge and code verifier
+// to prevent CSRF attacks. A unique code challenge and code verifier should be generated
+// by the caller at runtime. See https://www.oauth.com/oauth2-servers/pkce/ for more info.
+func TokenSourceWithPKCE(ctx context.Context, config *oauth2.Config, state string, authHandler AuthorizationHandler, pkce *PKCEParams) oauth2.TokenSource {
+ return oauth2.ReuseTokenSource(nil, authHandlerSource{config: config, ctx: ctx, authHandler: authHandler, state: state, pkce: pkce})
+}
+
// TokenSource returns an oauth2.TokenSource that fetches access tokens
// using 3-legged-OAuth flow.
//
@@ -33,7 +58,7 @@
// 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})
+ return TokenSourceWithPKCE(ctx, config, state, authHandler, nil)
}
type authHandlerSource struct {
@@ -41,10 +66,17 @@
config *oauth2.Config
authHandler AuthorizationHandler
state string
+ pkce *PKCEParams
}
func (source authHandlerSource) Token() (*oauth2.Token, error) {
- url := source.config.AuthCodeURL(source.state)
+ // Step 1: Obtain auth code.
+ var authCodeUrlOptions []oauth2.AuthCodeOption
+ if source.pkce != nil && source.pkce.Challenge != "" && source.pkce.ChallengeMethod != "" {
+ authCodeUrlOptions = []oauth2.AuthCodeOption{oauth2.SetAuthURLParam(codeChallengeKey, source.pkce.Challenge),
+ oauth2.SetAuthURLParam(codeChallengeMethodKey, source.pkce.ChallengeMethod)}
+ }
+ url := source.config.AuthCodeURL(source.state, authCodeUrlOptions...)
code, state, err := source.authHandler(url)
if err != nil {
return nil, err
@@ -52,5 +84,11 @@
if state != source.state {
return nil, errors.New("state mismatch in 3-legged-OAuth flow")
}
- return source.config.Exchange(source.ctx, code)
+
+ // Step 2: Exchange auth code for access token.
+ var exchangeOptions []oauth2.AuthCodeOption
+ if source.pkce != nil && source.pkce.Verifier != "" {
+ exchangeOptions = []oauth2.AuthCodeOption{oauth2.SetAuthURLParam(codeVerifierKey, source.pkce.Verifier)}
+ }
+ return source.config.Exchange(source.ctx, code, exchangeOptions...)
}
diff --git a/authhandler/authhandler_test.go b/authhandler/authhandler_test.go
index 084198f..ad19804 100644
--- a/authhandler/authhandler_test.go
+++ b/authhandler/authhandler_test.go
@@ -97,3 +97,61 @@
t.Errorf("err = %q; want %q", err, want_err)
}
}
+
+func TestTokenExchangeWithPKCE_Success(t *testing.T) {
+ authhandler := func(authCodeURL string) (string, string, error) {
+ if authCodeURL == "testAuthCodeURL?client_id=testClientID&code_challenge=codeChallenge&code_challenge_method=plain&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" && r.Form.Get("code_verifier") == "codeChallenge" {
+ w.Header().Set("Content-Type", "application/json")
+ w.Write([]byte(`{
+ "access_token": "90d64460d14870c08c81352a05dedd3465940a7c",
+ "scope": "pubsub",
+ "token_type": "bearer",
+ "expires_in": 3600
+ }`))
+ }
+ }))
+ defer ts.Close()
+
+ conf := &oauth2.Config{
+ ClientID: "testClientID",
+ Scopes: []string{"pubsub"},
+ Endpoint: oauth2.Endpoint{
+ AuthURL: "testAuthCodeURL",
+ TokenURL: ts.URL,
+ },
+ }
+ pkce := PKCEParams{
+ Challenge: "codeChallenge",
+ ChallengeMethod: "plain",
+ Verifier: "codeChallenge",
+ }
+
+ tok, err := TokenSourceWithPKCE(context.Background(), conf, "testState", authhandler, &pkce).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)
+ }
+}
diff --git a/google/default.go b/google/default.go
index 024a104..7ed02cd 100644
--- a/google/default.go
+++ b/google/default.go
@@ -54,11 +54,14 @@
// Optional.
Subject string
- // AuthHandler is the AuthorizationHandler used for 3-legged OAuth flow. Optional.
+ // AuthHandler is the AuthorizationHandler used for 3-legged OAuth flow. Required for 3LO flow.
AuthHandler authhandler.AuthorizationHandler
- // State is a unique string used with AuthHandler. Optional.
+ // State is a unique string used with AuthHandler. Required for 3LO flow.
State string
+
+ // PKCE is used to support PKCE flow. Optional for 3LO flow.
+ PKCE *authhandler.PKCEParams
}
func (params CredentialsParams) deepCopy() CredentialsParams {
@@ -176,7 +179,7 @@
if config != nil {
return &Credentials{
ProjectID: "",
- TokenSource: authhandler.TokenSource(ctx, config, params.State, params.AuthHandler),
+ TokenSource: authhandler.TokenSourceWithPKCE(ctx, config, params.State, params.AuthHandler, params.PKCE),
JSON: jsonData,
}, nil
}
