diff --git a/native/cpp/CommonCpp/NativeModules/CommRustModule.h b/native/cpp/CommonCpp/NativeModules/CommRustModule.h
--- a/native/cpp/CommonCpp/NativeModules/CommRustModule.h
+++ b/native/cpp/CommonCpp/NativeModules/CommRustModule.h
@@ -125,6 +125,11 @@
       jsi::String notifPrekeySignature,
       jsi::Array contentOneTimeKeys,
       jsi::Array notifOneTimeKeys) override;
+  virtual jsi::Value logInExistingDevice(
+      jsi::Runtime &rt,
+      jsi::String userID,
+      jsi::String deviceID,
+      jsi::String challengeResponse) override;
   virtual jsi::Value findUserIDForWalletAddress(
       jsi::Runtime &rt,
       jsi::String walletAddress) override;
diff --git a/native/cpp/CommonCpp/NativeModules/CommRustModule.cpp b/native/cpp/CommonCpp/NativeModules/CommRustModule.cpp
--- a/native/cpp/CommonCpp/NativeModules/CommRustModule.cpp
+++ b/native/cpp/CommonCpp/NativeModules/CommRustModule.cpp
@@ -596,7 +596,33 @@
               [error, promise]() { promise->reject(error); });
         }
       });
-  return jsi::Value::undefined();
+}
+
+jsi::Value CommRustModule::logInExistingDevice(
+    jsi::Runtime &rt,
+    jsi::String userID,
+    jsi::String deviceID,
+    jsi::String challengeResponse) {
+  auto userIDRust = jsiStringToRustString(userID, rt);
+  auto deviceIDRust = jsiStringToRustString(deviceID, rt);
+  auto challengeResponseRust = jsiStringToRustString(challengeResponse, rt);
+
+  return createPromiseAsJSIValue(
+      rt, [=, this](jsi::Runtime &innerRt, std::shared_ptr<Promise> promise) {
+        std::string error;
+        try {
+          auto currentID = RustPromiseManager::instance.addPromise(
+              {promise, this->jsInvoker_, innerRt});
+          identityLogInExistingDevice(
+              userIDRust, deviceIDRust, challengeResponseRust, currentID);
+        } catch (const std::exception &e) {
+          error = e.what();
+        };
+        if (!error.empty()) {
+          this->jsInvoker_->invokeAsync(
+              [error, promise]() { promise->reject(error); });
+        }
+      });
 }
 
 jsi::Value CommRustModule::findUserIDForWalletAddress(
diff --git a/native/cpp/CommonCpp/_generated/rustJSI-generated.cpp b/native/cpp/CommonCpp/_generated/rustJSI-generated.cpp
--- a/native/cpp/CommonCpp/_generated/rustJSI-generated.cpp
+++ b/native/cpp/CommonCpp/_generated/rustJSI-generated.cpp
@@ -60,6 +60,9 @@
 static jsi::Value __hostFunction_CommRustModuleSchemaCxxSpecJSI_uploadSecondaryDeviceKeysAndLogIn(jsi::Runtime &rt, TurboModule &turboModule, const jsi::Value* args, size_t count) {
   return static_cast<CommRustModuleSchemaCxxSpecJSI *>(&turboModule)->uploadSecondaryDeviceKeysAndLogIn(rt, args[0].asString(rt), args[1].asString(rt), args[2].asString(rt), args[3].asString(rt), args[4].asString(rt), args[5].asString(rt), args[6].asString(rt), args[7].asString(rt), args[8].asObject(rt).asArray(rt), args[9].asObject(rt).asArray(rt));
 }
+static jsi::Value __hostFunction_CommRustModuleSchemaCxxSpecJSI_logInExistingDevice(jsi::Runtime &rt, TurboModule &turboModule, const jsi::Value* args, size_t count) {
+  return static_cast<CommRustModuleSchemaCxxSpecJSI *>(&turboModule)->logInExistingDevice(rt, args[0].asString(rt), args[1].asString(rt), args[2].asString(rt));
+}
 static jsi::Value __hostFunction_CommRustModuleSchemaCxxSpecJSI_findUserIDForWalletAddress(jsi::Runtime &rt, TurboModule &turboModule, const jsi::Value* args, size_t count) {
   return static_cast<CommRustModuleSchemaCxxSpecJSI *>(&turboModule)->findUserIDForWalletAddress(rt, args[0].asString(rt));
 }
@@ -94,6 +97,7 @@
   methodMap_["getDeviceListForUser"] = MethodMetadata {5, __hostFunction_CommRustModuleSchemaCxxSpecJSI_getDeviceListForUser};
   methodMap_["updateDeviceList"] = MethodMetadata {4, __hostFunction_CommRustModuleSchemaCxxSpecJSI_updateDeviceList};
   methodMap_["uploadSecondaryDeviceKeysAndLogIn"] = MethodMetadata {10, __hostFunction_CommRustModuleSchemaCxxSpecJSI_uploadSecondaryDeviceKeysAndLogIn};
+  methodMap_["logInExistingDevice"] = MethodMetadata {3, __hostFunction_CommRustModuleSchemaCxxSpecJSI_logInExistingDevice};
   methodMap_["findUserIDForWalletAddress"] = MethodMetadata {1, __hostFunction_CommRustModuleSchemaCxxSpecJSI_findUserIDForWalletAddress};
   methodMap_["findUserIDForUsername"] = MethodMetadata {1, __hostFunction_CommRustModuleSchemaCxxSpecJSI_findUserIDForUsername};
   methodMap_["getFarcasterUsers"] = MethodMetadata {1, __hostFunction_CommRustModuleSchemaCxxSpecJSI_getFarcasterUsers};
diff --git a/native/cpp/CommonCpp/_generated/rustJSI.h b/native/cpp/CommonCpp/_generated/rustJSI.h
--- a/native/cpp/CommonCpp/_generated/rustJSI.h
+++ b/native/cpp/CommonCpp/_generated/rustJSI.h
@@ -36,6 +36,7 @@
   virtual jsi::Value getDeviceListForUser(jsi::Runtime &rt, jsi::String authUserID, jsi::String authDeviceID, jsi::String authAccessToken, jsi::String userID, std::optional<double> sinceTimestamp) = 0;
   virtual jsi::Value updateDeviceList(jsi::Runtime &rt, jsi::String authUserID, jsi::String authDeviceID, jsi::String authAccessToken, jsi::String updatePayload) = 0;
   virtual jsi::Value uploadSecondaryDeviceKeysAndLogIn(jsi::Runtime &rt, jsi::String userID, jsi::String challengeResponse, jsi::String keyPayload, jsi::String keyPayloadSignature, jsi::String contentPrekey, jsi::String contentPrekeySignature, jsi::String notifPrekey, jsi::String notifPrekeySignature, jsi::Array contentOneTimeKeys, jsi::Array notifOneTimeKeys) = 0;
+  virtual jsi::Value logInExistingDevice(jsi::Runtime &rt, jsi::String userID, jsi::String deviceID, jsi::String challengeResponse) = 0;
   virtual jsi::Value findUserIDForWalletAddress(jsi::Runtime &rt, jsi::String walletAddress) = 0;
   virtual jsi::Value findUserIDForUsername(jsi::Runtime &rt, jsi::String username) = 0;
   virtual jsi::Value getFarcasterUsers(jsi::Runtime &rt, jsi::Array farcasterIDs) = 0;
@@ -190,6 +191,14 @@
       return bridging::callFromJs<jsi::Value>(
           rt, &T::uploadSecondaryDeviceKeysAndLogIn, jsInvoker_, instance_, std::move(userID), std::move(challengeResponse), std::move(keyPayload), std::move(keyPayloadSignature), std::move(contentPrekey), std::move(contentPrekeySignature), std::move(notifPrekey), std::move(notifPrekeySignature), std::move(contentOneTimeKeys), std::move(notifOneTimeKeys));
     }
+    jsi::Value logInExistingDevice(jsi::Runtime &rt, jsi::String userID, jsi::String deviceID, jsi::String challengeResponse) override {
+      static_assert(
+          bridging::getParameterCount(&T::logInExistingDevice) == 4,
+          "Expected logInExistingDevice(...) to have 4 parameters");
+
+      return bridging::callFromJs<jsi::Value>(
+          rt, &T::logInExistingDevice, jsInvoker_, instance_, std::move(userID), std::move(deviceID), std::move(challengeResponse));
+    }
     jsi::Value findUserIDForWalletAddress(jsi::Runtime &rt, jsi::String walletAddress) override {
       static_assert(
           bridging::getParameterCount(&T::findUserIDForWalletAddress) == 2,
diff --git a/native/schema/CommRustModuleSchema.js b/native/schema/CommRustModuleSchema.js
--- a/native/schema/CommRustModuleSchema.js
+++ b/native/schema/CommRustModuleSchema.js
@@ -120,6 +120,11 @@
     contentOneTimeKeys: $ReadOnlyArray<string>,
     notifOneTimeKeys: $ReadOnlyArray<string>,
   ) => Promise<string>;
+  +logInExistingDevice: (
+    userID: string,
+    deviceID: string,
+    challengeResponse: string,
+  ) => Promise<string>;
   +findUserIDForWalletAddress: (walletAddress: string) => Promise<string>;
   +findUserIDForUsername: (username: string) => Promise<string>;
   +getFarcasterUsers: (farcasterIDs: $ReadOnlyArray<string>) => Promise<string>;