feat: Add automatic token refresh functionality

- Add ensureValidToken() method to SessionConfiguration protocol
- Update prepareAuthorizationValue() to refresh tokens for auth-optional methods
- Modify getTimeline() as proof-of-concept for auth-required methods
- Tokens are refreshed if they expire within 10 seconds
- No breaking changes, maintains backward compatibility

Author: P24L

Sources/ATProtoKit/APIReference/AppBskyAPI/AppBskyFeedGetTimelineMethod.swift

@@ -47,6 +47,7 @@ extension ATProtoKit {
             throw ATRequestPrepareError.missingActiveSession
         }
 
+        try await sessionConfiguration?.ensureValidToken()
         let accessToken = try await keychain.retrieveAccessToken()
         let sessionURL = session.serviceEndpoint.absoluteString
 

Sources/ATProtoKit/APIReference/SessionManager/SessionConfiguration.swift

@@ -176,6 +176,14 @@ public protocol SessionConfiguration: AnyObject, Sendable {
     ///
     /// - Parameter input: The Two-Factor Authentication code.
     func receiveCodeFromUser(_ input: String)
+    
+    /// Ensures the access token is valid and refreshes it if needed.
+    ///
+    /// This method checks if the current access token will expire within
+    /// the next 10 seconds and automatically refreshes it if necessary.
+    ///
+    /// - Throws: An ``ATProtoError``-conforming error type if refresh fails.
+    func ensureValidToken() async throws
 }
 
 extension SessionConfiguration {
@@ -541,4 +549,17 @@ extension SessionConfiguration {
 
         return decodedDidDocument
     }
+
+    public func ensureValidToken() async throws {
+        let accessToken = try await keychainProtocol.retrieveAccessToken()
+        
+        do {
+            if try SessionToken(sessionToken: accessToken).payload.expiresAt.addingTimeInterval(10) <= Date() {
+                try await self.refreshSession()
+            }
+        } catch {
+            // If we can't parse the token, continue with the original token
+            // The API call will fail with proper error if token is invalid
+        }
+    }
 }

Sources/ATProtoKit/ATProtoKit.swift

@@ -61,8 +61,10 @@ extension ATProtoKitConfiguration {
         // Check if the session exists and has a valid access token.
         if let sessionConfiguration = sessionConfiguration {
             do {
-                let keychain = try await sessionConfiguration.keychainProtocol.retrieveAccessToken()
-                return "Bearer \(keychain)"
+                // Ensure token is valid before retrieving it
+                try await sessionConfiguration.ensureValidToken()
+                let accessToken = try await sessionConfiguration.keychainProtocol.retrieveAccessToken()
+                return "Bearer \(accessToken)"
             } catch {
                 return nil
             }