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# SDK Core & Authentication
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The Facebook SDK core module provides essential functionality for SDK initialization, configuration, access token management, and Graph API access. This is the foundation that all other Facebook SDK modules depend on.
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## SDK Initialization
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The Facebook SDK must be initialized before use, typically in your Application class.
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```kotlin { .api }
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object FacebookSdk {
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    fun sdkInitialize(applicationContext: Context)
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    fun sdkInitialize(applicationContext: Context, callback: InitializeCallback?)
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    fun isInitialized(): Boolean
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    fun fullyInitialize()
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    fun isFullyInitialized(): Boolean
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}
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interface InitializeCallback {
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    fun onInitialized()
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}
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```
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### Usage Example
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```kotlin
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class MyApplication : Application() {
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    override fun onCreate() {
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        super.onCreate()
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        FacebookSdk.sdkInitialize(applicationContext) {
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            // SDK initialization complete
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            Log.d("Facebook", "SDK initialized")
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        }
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    }
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}
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```
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## SDK Configuration
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```kotlin { .api }
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object FacebookSdk {
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    // Application configuration
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    fun getApplicationId(): String
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    fun setApplicationId(applicationId: String)
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    fun getApplicationName(): String?
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    fun setApplicationName(applicationName: String?)
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    fun getClientToken(): String
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    fun setClientToken(clientToken: String?)
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    // Version information
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    fun getSdkVersion(): String
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    fun getGraphApiVersion(): String
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    fun setGraphApiVersion(graphApiVersion: String)
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    // Context and execution
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    fun getApplicationContext(): Context
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    fun getExecutor(): Executor
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    fun setExecutor(executor: Executor)
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    // Debugging and logging
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    fun isDebugEnabled(): Boolean
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    fun setIsDebugEnabled(enabled: Boolean)
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    fun getLoggingBehaviors(): Set<LoggingBehavior>
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    fun addLoggingBehavior(behavior: LoggingBehavior)
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    fun removeLoggingBehavior(behavior: LoggingBehavior)
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    fun clearLoggingBehaviors()
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    fun isLoggingBehaviorEnabled(behavior: LoggingBehavior): Boolean
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}
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enum class LoggingBehavior {
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    REQUESTS,
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    INCLUDE_ACCESS_TOKENS,
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    INCLUDE_RAW_RESPONSES,
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    CACHE,
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    APP_EVENTS,
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    DEVELOPER_ERRORS,
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    GRAPH_API_DEBUG_WARNING,
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    GRAPH_API_DEBUG_INFO
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}
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```
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## Access Token Management
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Access tokens are central to Facebook API interactions, representing user authentication and permissions.
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```kotlin { .api }
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class AccessToken(
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    accessToken: String,
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    applicationId: String,
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    userId: String,
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    permissions: Collection<String?>?,
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    declinedPermissions: Collection<String?>?,
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    expiredPermissions: Collection<String?>?,
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    accessTokenSource: AccessTokenSource?,
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    expirationTime: Date?,
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    lastRefreshTime: Date?,
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    dataAccessExpirationTime: Date?,
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    graphDomain: String? = "facebook"
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) {
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    val token: String
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    val applicationId: String
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    val userId: String
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    val permissions: Set<String?>
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    val declinedPermissions: Set<String?>
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    val expiredPermissions: Set<String?>
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    val expires: Date
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    val lastRefresh: Date
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    val dataAccessExpirationTime: Date
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    val source: AccessTokenSource
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    val graphDomain: String?
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    // Token status
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    val isExpired: Boolean
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    val isDataAccessExpired: Boolean
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    val isInstagramToken: Boolean
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    companion object {
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        // Current token management
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        fun getCurrentAccessToken(): AccessToken?
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        fun setCurrentAccessToken(accessToken: AccessToken?)
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        fun isCurrentAccessTokenActive(): Boolean
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        fun isDataAccessActive(): Boolean
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        fun isLoggedInWithInstagram(): Boolean
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        fun expireCurrentAccessToken()
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        // Token refresh
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        fun refreshCurrentAccessTokenAsync()
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        fun refreshCurrentAccessTokenAsync(callback: AccessTokenRefreshCallback?)
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        // Token creation
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        fun createFromNativeLinkingIntent(
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            intent: Intent,
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            applicationId: String,
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            accessTokenCallback: AccessTokenCreationCallback
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        )
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    }
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}
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enum class AccessTokenSource {
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    FACEBOOK_APPLICATION_WEB,
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    FACEBOOK_APPLICATION_NATIVE,
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    FACEBOOK_APPLICATION_SERVICE,
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    WEB_VIEW,
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    CHROME_CUSTOM_TAB,
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    INSTAGRAM_APPLICATION_WEB,
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    INSTAGRAM_CUSTOM_CHROME_TAB,
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    INSTAGRAM_WEB_VIEW
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}
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interface AccessTokenRefreshCallback {
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    fun OnTokenRefreshed(accessToken: AccessToken?)
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    fun OnTokenRefreshFailed(exception: FacebookException?)
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}
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interface AccessTokenCreationCallback {
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    fun onSuccess(token: AccessToken?)
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    fun onError(error: FacebookException?)
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}
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```
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### Access Token Usage Example
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```kotlin
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// Check if user is logged in
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if (AccessToken.isCurrentAccessTokenActive()) {
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    val currentToken = AccessToken.getCurrentAccessToken()
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    val userId = currentToken?.userId
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    val permissions = currentToken?.permissions
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    // Use the token for API calls
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    makeGraphRequest(currentToken)
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} else {
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    // User needs to log in
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    initiateLogin()
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}
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// Refresh current token
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AccessToken.refreshCurrentAccessTokenAsync { accessToken ->
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    if (accessToken != null) {
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        // Token refreshed successfully
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        Log.d("Facebook", "Token refreshed for user: ${accessToken.userId}")
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    } else {
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        // Token refresh failed
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        Log.e("Facebook", "Failed to refresh token")
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    }
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}
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```
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## User Profile Management
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```kotlin { .api }
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class Profile(
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    id: String?,
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    firstName: String?,
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    middleName: String?,
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    lastName: String?,
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    name: String?,
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    linkUri: Uri?,
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    pictureUri: Uri?
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) {
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    val id: String?
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    val firstName: String?
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    val middleName: String?
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    val lastName: String?
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    val name: String?
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    val linkUri: Uri?
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    val pictureUri: Uri?
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    companion object {
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        fun getCurrentProfile(): Profile?
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        fun setCurrentProfile(profile: Profile?)
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        fun fetchProfileForCurrentAccessToken()
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    }
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}
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abstract class ProfileTracker {
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    val isTracking: Boolean
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    fun startTracking()
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    fun stopTracking()
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    protected abstract fun onCurrentProfileChanged(
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        oldProfile: Profile?,
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        currentProfile: Profile?
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    )
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}
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```
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## Authentication Tokens (OpenID Connect)
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For apps using OpenID Connect authentication:
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```kotlin { .api }
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class AuthenticationToken(
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    token: String,
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    nonce: String,
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    graphDomain: String
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) {
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    val token: String
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    val nonce: String
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    val graphDomain: String
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    val header: AuthenticationTokenHeader
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    val claims: AuthenticationTokenClaims
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    companion object {
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        fun getCurrentAuthenticationToken(): AuthenticationToken?
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        fun setCurrentAuthenticationToken(token: AuthenticationToken?)
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    }
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}
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class AuthenticationTokenClaims(
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    encodedClaims: String,
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    expectedNonce: String
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) {
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    val jti: String?
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    val iss: String?
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    val aud: String?
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    val nonce: String?
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    val exp: Long
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    val iat: Long
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    val sub: String?
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    val name: String?
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    val givenName: String?
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    val middleName: String?
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    val familyName: String?
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    val email: String?
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    val picture: String?
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    val userFriends: List<String>?
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    val userBirthday: String?
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    val userAgeRange: Map<String, Int>?
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    val userHometown: Map<String, String>?
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    val userLocation: Map<String, String>?
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    val userGender: String?
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    val userLink: String?
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}
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class AuthenticationTokenHeader(encodedHeader: String) {
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    val alg: String?
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    val typ: String?
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    val kid: String?
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}
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```
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## Exception Handling
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```kotlin { .api }
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open class FacebookException(message: String?) : RuntimeException(message)
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class FacebookSdkNotInitializedException(message: String?) : FacebookException(message)
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class FacebookAuthorizationException(message: String?) : FacebookException(message)
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class FacebookOperationCanceledException(message: String?) : FacebookException(message)
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class FacebookServiceException(
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    error: FacebookRequestError,
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    errorMessage: String?
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) : FacebookException(errorMessage)
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class FacebookGraphResponseException(
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    response: GraphResponse,
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    message: String?
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) : FacebookException(message) {
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    val graphResponse: GraphResponse
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}
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class FacebookRequestError(
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    requestStatusCode: Int,
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    errorCode: Int,
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    errorType: String?,
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    errorMessage: String?
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) {
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    val requestStatusCode: Int
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    val errorCode: Int
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    val errorType: String?
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    val errorMessage: String?
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    val errorUserMessage: String?
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    val errorUserTitle: String?
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    val requestResult: JSONObject?
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    enum class Category {
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        LOGIN_RECOVERABLE,
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        OTHER,
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        TRANSIENT
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    }
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    val category: Category
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}
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```
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## Callback Management
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```kotlin { .api }
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interface CallbackManager {
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    fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?): Boolean
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    object Factory {
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        fun create(): CallbackManager
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    }
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}
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interface FacebookCallback<T> {
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    fun onSuccess(result: T)
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    fun onCancel()
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    fun onError(error: FacebookException)
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}
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```
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### Example: Handling Activity Results
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```kotlin
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class MainActivity : AppCompatActivity() {
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    private lateinit var callbackManager: CallbackManager
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    override fun onCreate(savedInstanceState: Bundle?) {
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        super.onCreate(savedInstanceState)
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        callbackManager = CallbackManager.Factory.create()
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        // Register callbacks for various Facebook operations
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        LoginManager.getInstance().registerCallback(callbackManager, loginCallback)
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        ShareDialog(this).registerCallback(callbackManager, shareCallback)
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    }
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    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
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        // This delegates to all registered Facebook callbacks
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        callbackManager.onActivityResult(requestCode, resultCode, data)
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        super.onActivityResult(requestCode, resultCode, data)
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    }
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}
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```
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## User Settings Management
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```kotlin { .api }
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object UserSettingsManager {
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    fun getAutoInitEnabled(): Boolean
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    fun setAutoInitEnabled(enabled: Boolean)
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    fun getAutoLogAppEventsEnabled(): Boolean
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    fun setAutoLogAppEventsEnabled(enabled: Boolean)
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    fun getAdvertiserIDCollectionEnabled(): Boolean
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    fun setAdvertiserIDCollectionEnabled(enabled: Boolean)
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    fun getCodelessSetupEnabled(): Boolean
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    fun getMonitorEnabled(): Boolean
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    fun setMonitorEnabled(enabled: Boolean)
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}
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```