Enable access for token refresh

Sources/Twift.swift

@@ -5,13 +5,28 @@ import Combine
 public class Twift: NSObject, ObservableObject {
   /// The type of authentication access for this Twift instance
   public private(set) var authenticationType: AuthenticationType
+  public var oauthUser: OAuth2User? {
+    switch authenticationType {
+      case .oauth2UserAuth(let user):
+        return user
+      default:
+        return nil
+    }
+  }
+
+  /// Optional callback to be performed after a successful token refresh.
+  private var refreshCompletion: (()-> Void)? = nil
 
   internal let decoder: JSONDecoder
   internal let encoder: JSONEncoder
 
   /// Initialise an instance with the specified authentication type
-  public init(_ authenticationType: AuthenticationType) {
+  public init(_ authenticationType: AuthenticationType, onRefresh: (()-> Void)? = nil) {
     self.authenticationType = authenticationType
+
+    if let refreshCompletion = onRefresh {
+        self.refreshCompletion = refreshCompletion
+    }
 
     self.decoder = Self.initializeDecoder()
     self.encoder = Self.initializeEncoder()
@@ -71,6 +86,7 @@ public class Twift: NSObject, ObservableObject {
   }
 
   /// Refreshes the OAuth 2.0 token, optionally forcing a refresh even if the token is still valid
+  /// After a successful refresh, a user-defined callback is performed. (optional)
   /// - Parameter onlyIfExpired: Set to false to force the token to refresh even if it hasn't yet expired.
   public func refreshOAuth2AccessToken(onlyIfExpired: Bool = true) async throws {
     guard case AuthenticationType.oauth2UserAuth(let oauthUser) = self.authenticationType else {
@@ -107,5 +123,9 @@ public class Twift: NSObject, ObservableObject {
     refreshedOAuthUser.clientId = clientId
 
     self.authenticationType = .oauth2UserAuth(refreshedOAuthUser)
+
+    if let userDefinedRefreshCompletion = refreshCompletion {
+      userDefinedRefreshCompletion()
+    }
   }
 }