android: secure token storage with keystore-backed encrypted prefs

android/app/src/main/java/ru/daemonlord/messenger/core/token/EncryptedPrefsTokenRepository.kt

@@ -0,0 +1,60 @@
+package ru.daemonlord.messenger.core.token
+
+import android.content.SharedPreferences
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import ru.daemonlord.messenger.di.TokenPrefs
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@Singleton
+class EncryptedPrefsTokenRepository @Inject constructor(
+    @TokenPrefs private val sharedPreferences: SharedPreferences,
+) : TokenRepository {
+
+    private val tokensFlow = MutableStateFlow(readTokens())
+
+    override fun observeTokens(): Flow<TokenBundle?> = tokensFlow.asStateFlow()
+
+    override suspend fun getTokens(): TokenBundle? = tokensFlow.value
+
+    override suspend fun saveTokens(tokens: TokenBundle) {
+        sharedPreferences.edit()
+            .putString(ACCESS_TOKEN_KEY, tokens.accessToken)
+            .putString(REFRESH_TOKEN_KEY, tokens.refreshToken)
+            .putLong(SAVED_AT_KEY, tokens.savedAtMillis)
+            .apply()
+        tokensFlow.value = tokens
+    }
+
+    override suspend fun clearTokens() {
+        sharedPreferences.edit()
+            .remove(ACCESS_TOKEN_KEY)
+            .remove(REFRESH_TOKEN_KEY)
+            .remove(SAVED_AT_KEY)
+            .apply()
+        tokensFlow.value = null
+    }
+
+    private fun readTokens(): TokenBundle? {
+        val access = sharedPreferences.getString(ACCESS_TOKEN_KEY, null)
+        val refresh = sharedPreferences.getString(REFRESH_TOKEN_KEY, null)
+        val savedAt = sharedPreferences.getLong(SAVED_AT_KEY, -1L)
+        if (access.isNullOrBlank() || refresh.isNullOrBlank() || savedAt <= 0L) {
+            return null
+        }
+        return TokenBundle(
+            accessToken = access,
+            refreshToken = refresh,
+            savedAtMillis = savedAt,
+        )
+    }
+
+    private companion object {
+        const val ACCESS_TOKEN_KEY = "access_token"
+        const val REFRESH_TOKEN_KEY = "refresh_token"
+        const val SAVED_AT_KEY = "tokens_saved_at"
+    }
+}
+

android/app/src/main/java/ru/daemonlord/messenger/di/Qualifiers.kt

@@ -13,3 +13,7 @@ annotation class RefreshAuthApi
 @Qualifier
 @Retention(AnnotationRetention.BINARY)
 annotation class IoDispatcher
+
+@Qualifier
+@Retention(AnnotationRetention.BINARY)
+annotation class TokenPrefs

android/app/src/main/java/ru/daemonlord/messenger/di/StorageModule.kt

@@ -1,16 +1,19 @@
 package ru.daemonlord.messenger.di
 
 import android.content.Context
+import android.content.SharedPreferences
 import androidx.datastore.core.DataStore
 import androidx.datastore.preferences.core.Preferences
 import androidx.datastore.preferences.core.PreferenceDataStoreFactory
 import androidx.datastore.preferences.preferencesDataStoreFile
+import androidx.security.crypto.EncryptedSharedPreferences
+import androidx.security.crypto.MasterKey
 import dagger.Module
 import dagger.Provides
 import dagger.hilt.InstallIn
 import dagger.hilt.android.qualifiers.ApplicationContext
 import dagger.hilt.components.SingletonComponent
-import ru.daemonlord.messenger.core.token.DataStoreTokenRepository
+import ru.daemonlord.messenger.core.token.EncryptedPrefsTokenRepository
 import ru.daemonlord.messenger.core.token.TokenRepository
 import javax.inject.Singleton
 
@@ -24,13 +27,31 @@ object StorageModule {
         @ApplicationContext context: Context,
     ): DataStore<Preferences> {
         return PreferenceDataStoreFactory.create(
-            produceFile = { context.preferencesDataStoreFile("messenger_tokens.preferences_pb") }
+            produceFile = { context.preferencesDataStoreFile("messenger_preferences.preferences_pb") }
+        )
+    }
+
+    @Provides
+    @Singleton
+    @TokenPrefs
+    fun provideTokenSharedPreferences(
+        @ApplicationContext context: Context,
+    ): SharedPreferences {
+        val masterKey = MasterKey.Builder(context)
+            .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
+            .build()
+        return EncryptedSharedPreferences.create(
+            context,
+            "messenger_secure_tokens",
+            masterKey,
+            EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
+            EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM,
         )
     }
 
     @Provides
     @Singleton
     fun provideTokenRepository(
-        repository: DataStoreTokenRepository,
+        repository: EncryptedPrefsTokenRepository,
     ): TokenRepository = repository
 }