fix(android): allow BuildConfig lookup when applicationId != namespace

android/build.gradle

@@ -81,6 +81,8 @@ dependencies {
   implementation 'io.reactivex.rxjava3:rxkotlin:3.0.1'
   implementation 'com.google.code.gson:gson:2.10.1'
   implementation 'com.frontegg.sdk:android:1.3.18'
+
+  testImplementation 'junit:junit:4.13.2'
 }
 
 if (isNewArchitectureEnabled()) {

android/src/main/java/com/frontegg/reactnative/Utils.kt

@@ -2,50 +2,114 @@ package com.frontegg.reactnative
 
 import android.app.Activity
 import android.content.Context
+import android.content.pm.PackageManager
 import android.util.Log
 
 
 const val TAG: String = "FronteggUtils"
 
+private const val BUILD_CONFIG_PACKAGE_META = "com.frontegg.reactnative.BUILD_CONFIG_PACKAGE"
+
 
 interface ActivityProvider {
     fun getActivity(): Activity?
 }
 
 val Context.fronteggConstants: FronteggConstants
     get() {
-        val packageName = this.packageName
-        val className = "$packageName.BuildConfig"
+        val buildConfigClass = resolveBuildConfigClass(this)
+
+        // Get the field from BuildConfig class
+        val baseUrl = safeGetValueFromBuildConfig(buildConfigClass, "FRONTEGG_DOMAIN", "")
+        val clientId = safeGetValueFromBuildConfig(buildConfigClass, "FRONTEGG_CLIENT_ID", "")
+
+        val applicationId =
+            safeGetNullableValueFromBuildConfig(buildConfigClass, "FRONTEGG_APPLICATION_ID", "")
+
+        val useAssetsLinks =
+            safeGetValueFromBuildConfig(buildConfigClass, "FRONTEGG_USE_ASSETS_LINKS", true)
+        val useChromeCustomTabs = safeGetValueFromBuildConfig(
+            buildConfigClass, "FRONTEGG_USE_CHROME_CUSTOM_TABS", true
+        )
+
+        return FronteggConstants(
+            baseUrl = baseUrl,
+            clientId = clientId,
+            applicationId = applicationId,
+            useAssetsLinks = useAssetsLinks,
+            useChromeCustomTabs = useChromeCustomTabs,
+            bundleId = this.packageName,
+        )
+    }
+
+/**
+ * Locate the host app's generated `BuildConfig` class.
+ *
+ * The class lives at `<javaPackage>.BuildConfig`, but apps whose `applicationId` differs from
+ * their AGP `namespace` (a common pattern for white-label / multi-flavor builds) need to
+ * override the lookup, since [Context.getPackageName] returns the `applicationId` at runtime
+ * while the generated `BuildConfig` is emitted under the `namespace`.
+ *
+ * Resolution order:
+ *  1. `<applicationContext.packageName>.BuildConfig` (the existing behaviour).
+ *  2. The value of the `com.frontegg.reactnative.BUILD_CONFIG_PACKAGE` `<meta-data>` entry on
+ *     `<application>` in `AndroidManifest.xml`, suffixed with `.BuildConfig`.
+ */
+private fun resolveBuildConfigClass(context: Context): Class<*> {
+    val candidates = buildConfigClassCandidates(
+        primaryPackageName = context.packageName,
+        fallbackPackageName = readFallbackBuildConfigPackage(context),
+    )
+
+    var lastError: ClassNotFoundException? = null
+    for (className in candidates) {
         try {
-            val buildConfigClass = Class.forName(className)
-
-            // Get the field from BuildConfig class
-            val baseUrl = safeGetValueFromBuildConfig(buildConfigClass, "FRONTEGG_DOMAIN", "")
-            val clientId = safeGetValueFromBuildConfig(buildConfigClass, "FRONTEGG_CLIENT_ID", "")
-
-            val applicationId =
-                safeGetNullableValueFromBuildConfig(buildConfigClass, "FRONTEGG_APPLICATION_ID", "")
-
-            val useAssetsLinks =
-                safeGetValueFromBuildConfig(buildConfigClass, "FRONTEGG_USE_ASSETS_LINKS", true)
-            val useChromeCustomTabs = safeGetValueFromBuildConfig(
-                buildConfigClass, "FRONTEGG_USE_CHROME_CUSTOM_TABS", true
-            )
-
-            return FronteggConstants(
-                baseUrl = baseUrl,
-                clientId = clientId,
-                applicationId = applicationId,
-                useAssetsLinks = useAssetsLinks,
-                useChromeCustomTabs = useChromeCustomTabs,
-                bundleId = this.packageName,
-            )
+            return Class.forName(className)
         } catch (e: ClassNotFoundException) {
-            Log.e(TAG, "Class not found: $className")
-            throw e
+            Log.w(TAG, "BuildConfig not found at $className, trying next candidate")
+            lastError = e
         }
     }
 
+    Log.e(
+        TAG,
+        "Could not locate host BuildConfig. Tried: ${candidates.joinToString()}. " +
+            "If applicationId differs from your android.namespace, add " +
+            "<meta-data android:name=\"$BUILD_CONFIG_PACKAGE_META\" " +
+            "android:value=\"your.java.package\" /> to <application> in AndroidManifest.xml."
+    )
+    throw lastError ?: ClassNotFoundException("BuildConfig not found for ${context.packageName}")
+}
+
+/**
+ * Pure-logic candidate list for `BuildConfig` class lookup. Extracted from
+ * [resolveBuildConfigClass] so it can be unit-tested without Android dependencies.
+ *
+ * Guarantees:
+ *  - `primaryPackageName` is always tried first.
+ *  - `fallbackPackageName`, if non-null and non-blank, is appended next.
+ *  - If both inputs produce the same candidate string, only the first occurrence is kept.
+ */
+internal fun buildConfigClassCandidates(
+    primaryPackageName: String,
+    fallbackPackageName: String?,
+): List<String> {
+    val candidates = LinkedHashSet<String>()
+    candidates.add("$primaryPackageName.BuildConfig")
+    fallbackPackageName?.takeIf { it.isNotBlank() }?.let {
+        candidates.add("$it.BuildConfig")
+    }
+    return candidates.toList()
+}
+
+private fun readFallbackBuildConfigPackage(context: Context): String? = runCatching {
+    val appInfo = context.packageManager.getApplicationInfo(
+        context.packageName,
+        PackageManager.GET_META_DATA,
+    )
+    appInfo.metaData?.getString(BUILD_CONFIG_PACKAGE_META)
+}.getOrNull()
+
 fun <T> safeGetNullableValueFromBuildConfig(
     buildConfigClass: Class<*>,
     name: String,

android/src/test/java/com/frontegg/reactnative/UtilsTest.kt

@@ -0,0 +1,53 @@
+package com.frontegg.reactnative
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class UtilsTest {
+
+    @Test
+    fun `single candidate when fallback is null`() {
+        val candidates = buildConfigClassCandidates(
+            primaryPackageName = "com.example.app",
+            fallbackPackageName = null,
+        )
+
+        assertEquals(listOf("com.example.app.BuildConfig"), candidates)
+    }
+
+    @Test
+    fun `single candidate when fallback is blank`() {
+        val candidates = buildConfigClassCandidates(
+            primaryPackageName = "com.example.app",
+            fallbackPackageName = "  ",
+        )
+
+        assertEquals(listOf("com.example.app.BuildConfig"), candidates)
+    }
+
+    @Test
+    fun `applicationId is always tried before fallback`() {
+        val candidates = buildConfigClassCandidates(
+            primaryPackageName = "com.example.app",
+            fallbackPackageName = "com.example.shared",
+        )
+
+        assertEquals(
+            listOf(
+                "com.example.app.BuildConfig",
+                "com.example.shared.BuildConfig",
+            ),
+            candidates,
+        )
+    }
+
+    @Test
+    fun `duplicate candidate is deduplicated when applicationId equals fallback`() {
+        val candidates = buildConfigClassCandidates(
+            primaryPackageName = "com.example.shared",
+            fallbackPackageName = "com.example.shared",
+        )
+
+        assertEquals(listOf("com.example.shared.BuildConfig"), candidates)
+    }
+}