diff --git a/server.go b/server.go
index e351a15..a48feb1 100644
--- a/server.go
+++ b/server.go
@@ -406,7 +406,7 @@ func GenerateSecret() string {
 
 	rand.Read(b)
 
-	return base64.RawStdEncoding.EncodeToString(b)
+	return base64.RawURLEncoding.EncodeToString(b)
 }
 
 func GenerateCodeChallenge(verifier string) string {