diff --git a/authhandler/authhandler.go b/authhandler/authhandler.go
index bc86531..9bc6cd7 100644
--- a/authhandler/authhandler.go
+++ b/authhandler/authhandler.go
@@ -24,9 +24,9 @@ const (
 
 // PKCEParams holds parameters to support PKCE.
 type PKCEParams struct {
-	CodeChallenge       string // The unpadded, base64-url-encoded string of the encrypted codeVerifier.
-	CodeChallengeMethod string // The encryption method (ex. S256).
-	CodeVerifier        string // The original, non-encrypted secret.
+	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
@@ -34,6 +34,15 @@ type PKCEParams struct {
 // 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.
 //
@@ -48,14 +57,6 @@ 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.
-//
-// The pkce parameter supports PKCE flow.
-// 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})
-}
-
-// Deprecated: Use TokenSourceWithPKCE instead.
 func TokenSource(ctx context.Context, config *oauth2.Config, state string, authHandler AuthorizationHandler) oauth2.TokenSource {
 	return TokenSourceWithPKCE(ctx, config, state, authHandler, nil)
 }
@@ -71,9 +72,9 @@ type authHandlerSource struct {
 func (source authHandlerSource) Token() (*oauth2.Token, error) {
 	// Step 1: Obtain auth code.
 	var authCodeUrlOptions []oauth2.AuthCodeOption
-	if source.pkce != nil {
-		authCodeUrlOptions = []oauth2.AuthCodeOption{oauth2.SetAuthURLParam(codeChallengeKey, source.pkce.CodeChallenge),
-			oauth2.SetAuthURLParam(codeChallengeMethodKey, source.pkce.CodeChallengeMethod)}
+	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)
@@ -86,8 +87,8 @@ func (source authHandlerSource) Token() (*oauth2.Token, error) {
 
 	// Step 2: Exchange auth code for access token.
 	var exchangeOptions []oauth2.AuthCodeOption
-	if source.pkce != nil {
-		exchangeOptions = []oauth2.AuthCodeOption{oauth2.SetAuthURLParam(codeVerifierKey, source.pkce.CodeVerifier)}
+	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 0e50e15..ad19804 100644
--- a/authhandler/authhandler_test.go
+++ b/authhandler/authhandler_test.go
@@ -129,9 +129,9 @@ func TestTokenExchangeWithPKCE_Success(t *testing.T) {
 		},
 	}
 	pkce := PKCEParams{
-		CodeChallenge:       "codeChallenge",
-		CodeChallengeMethod: "plain",
-		CodeVerifier:        "codeChallenge",
+		Challenge:       "codeChallenge",
+		ChallengeMethod: "plain",
+		Verifier:        "codeChallenge",
 	}
 
 	tok, err := TokenSourceWithPKCE(context.Background(), conf, "testState", authhandler, &pkce).Token()