diff --git a/quiche/blind_sign_auth/proto/auth_and_sign.proto b/quiche/blind_sign_auth/proto/auth_and_sign.proto
index 7089dfb..b35c285 100644
--- a/quiche/blind_sign_auth/proto/auth_and_sign.proto
+++ b/quiche/blind_sign_auth/proto/auth_and_sign.proto
@@ -21,9 +21,9 @@
 import "quiche/blind_sign_auth/proto/public_metadata.proto";
 
 // Client is requesting to auth using the provided auth token.
-// Next ID: 14
+// Next ID: 15
 message AuthAndSignRequest {
-  reserved 3;
+  reserved 3, 13;
 
   // A 'bearer' oauth token to be validated.
   // https://datatracker.ietf.org/doc/html/rfc6750#section-6.1.1
@@ -57,8 +57,10 @@
   // PUBLIC_METADATA.
   int64 key_version = 12 ;
 
-  // Only set one of this or public_metadata_info.
-  bytes binary_public_metadata = 13 ;
+  // Only set one of this or public_metadata_info. Uses IETF privacy pass
+  // extensions spec for format.
+  bytes public_metadata_extensions = 14
+      ;
 }
 
 message AuthAndSignResponse {
diff --git a/quiche/blind_sign_auth/proto/get_initial_data.proto b/quiche/blind_sign_auth/proto/get_initial_data.proto
index bcbd834..6b98745 100644
--- a/quiche/blind_sign_auth/proto/get_initial_data.proto
+++ b/quiche/blind_sign_auth/proto/get_initial_data.proto
@@ -48,6 +48,8 @@
 // Contains data needed to perform blind signing and prepare for calling
 // AuthAndSign.
 message GetInitialDataResponse {
+  reserved 4;
+
   private_membership.anonymous_tokens.RSABlindSignaturePublicKey
       at_public_metadata_public_key = 1;
 
@@ -58,7 +60,11 @@
   // if the service_type input requires it.
   privacy.ppn.PrepareAttestationData attestation = 3;
 
-  // General public metadata. Use metadata deserializer to inspect. Only set one
-  // of this or public_metadata_info.
-  bytes binary_public_metadata = 4 ;
+  // Data needed to support the privacy pass specification.
+  message PrivacyPassData {
+    bytes token_key_id = 1;
+    bytes public_metadata_extensions = 2
+        ;
+  }
+  PrivacyPassData privacy_pass_data = 5;
 }