Simplify list-MFA-keys RPC

Turns out clients only actually want the metadata, repeating the crypto
parameters is useless

service/src/main/java/org/whispersystems/textsecuregcm/grpc/AccountsGrpcService.java

@@ -53,6 +53,7 @@ import org.signal.chat.account.GetEntitlementsRequest;
 import org.signal.chat.account.GetEntitlementsResponse;
 import org.signal.chat.account.ListMfaKeysRequest;
 import org.signal.chat.account.ListMfaKeysResponse;
+import org.signal.chat.account.ListMfaKeysResponse.MfaKeyMetadata.MfaKeyType;
 import org.signal.chat.account.RegistrationLockFailure;
 import org.signal.chat.account.RemoveMfaKeyRequest;
 import org.signal.chat.account.RemoveMfaKeyResponse;
@@ -612,14 +613,13 @@ public class AccountsGrpcService extends SimpleAccountsGrpc.AccountsImplBase {
     getAuthenticatedAccount().getMfaKeys().forEach((keyId, mfaKey) -> {
       assert mfaKey.metadataCiphertext() != null;
 
-      ListMfaKeysResponse.MfaKeyMetadata.Builder metadataBuilder = ListMfaKeysResponse.MfaKeyMetadata.newBuilder()
-          .setMetadataCiphertext(ByteString.copyFrom(mfaKey.metadataCiphertext()));
-
-      switch (mfaKey) {
-        case AnnotatedTotpKey k -> metadataBuilder.setTotpParameters(toGrpcTotpParameters(k.totpKey().totpParameters()));
-      }
-
-      responseBuilder.putKeys(keyId, metadataBuilder.build());
+      responseBuilder.putKeys(
+          keyId,
+          ListMfaKeysResponse.MfaKeyMetadata.newBuilder()
+              .setMetadataCiphertext(ByteString.copyFrom(mfaKey.metadataCiphertext()))
+              .setType(switch (mfaKey) {
+                  case AnnotatedTotpKey _ -> MfaKeyType.MFA_KEY_TYPE_TOTP;
+              }).build());
     });
 
     return responseBuilder.build();

service/src/main/proto/org/signal/chat/account.proto

@@ -575,13 +575,16 @@ message ListMfaKeysRequest {}
 
 message ListMfaKeysResponse {
   message MfaKeyMetadata {
-    // The user-provided ciphertext for metadata associated with this MFA key
+    enum MfaKeyType {
+      MFA_KEY_TYPE_UNSPECIFIED = 0;
+      MFA_KEY_TYPE_TOTP = 1;
+    }
+
+    /// The user-provided ciphertext for metadata associated with this MFA key
     bytes metadata_ciphertext = 1 [(require.exactlySize) = 160];
 
-    oneof mfa_key {
-      // The TOTP parameters associated with this key, which is a TOTP key
-      TotpParameters totp_parameters = 2;
-    }
+    /// The type of MFA factor this key is for
+    MfaKeyType type = 2;
   }
 
   map<uint32, MfaKeyMetadata> keys = 1;

service/src/test/java/org/whispersystems/textsecuregcm/grpc/AccountsGrpcServiceTest.java

@@ -92,6 +92,7 @@ import org.signal.chat.account.SetZkCredentialKeyResponse;
 import org.signal.chat.account.StaleDevices;
 import org.signal.chat.account.TotpParameters;
 import org.signal.chat.account.UsernameNotAvailable;
+import org.signal.chat.account.ListMfaKeysResponse.MfaKeyMetadata.MfaKeyType;
 import org.signal.chat.common.AccountIdentifiers;
 import org.signal.chat.common.EcSignedPreKey;
 import org.signal.chat.common.KemSignedPreKey;
@@ -1236,15 +1237,9 @@ class AccountsGrpcServiceTest extends SimpleBaseGrpcTest<AccountsGrpcService, Ac
     final ListMfaKeysResponse response =
         authenticatedServiceStub().listMfaKeys(ListMfaKeysRequest.getDefaultInstance());
 
-    final TotpParameters expectedTotpParameters = TotpParameters.newBuilder()
-        .setAlgorithm(AccountsManager.TOTP.getAlgorithm())
-        .setPasswordLength(AccountsManager.TOTP.getPasswordLength())
-        .setTimeStepSeconds(Math.toIntExact(AccountsManager.TOTP.getTimeStep().toSeconds()))
-        .build();
-
     final Map<Integer, ListMfaKeysResponse.MfaKeyMetadata> expectedTotpKeys = totpKeys.entrySet().stream()
         .collect(Collectors.toMap(entry -> entry.getKey().intValue(), entry -> ListMfaKeysResponse.MfaKeyMetadata.newBuilder()
-            .setTotpParameters(expectedTotpParameters)
+            .setType(MfaKeyType.MFA_KEY_TYPE_TOTP)
             .setMetadataCiphertext(ByteString.copyFrom(entry.getValue().metadataCiphertext()))
             .build()));