OAuth session persists via DPAPI; sign-in lives in the Start Stream dialog; add xUnit test project (6 passing)

Services/YouTubeAuthService.cs

@@ -19,14 +19,24 @@ public class YouTubeAuthService
 
     private readonly string _clientId;
     private readonly string _clientSecret;
-    private readonly HttpClient _http = new();
+    private readonly HttpClient _http;
+    private readonly Action<YouTubeChannel>? _sessionChanged;
 
     public YouTubeChannel? CurrentChannel { get; private set; }
 
-    public YouTubeAuthService(string clientId, string clientSecret)
+    public YouTubeAuthService(string clientId, string clientSecret, HttpClient? http = null,
+        Action<YouTubeChannel>? sessionChanged = null)
     {
         _clientId = clientId;
         _clientSecret = clientSecret;
+        _http = http ?? new HttpClient();
+        _sessionChanged = sessionChanged;
+    }
+
+    /// <summary>Replaces the current session (used when a saved token loads at startup).</summary>
+    public void SetSession(YouTubeChannel channel)
+    {
+        CurrentChannel = channel;
     }
 
     public string GetAuthorizationUrl(string redirectUri)
@@ -136,6 +146,7 @@ public class YouTubeAuthService
 
         CurrentChannel.AccessToken = tokenData.GetProperty("access_token").GetString()!;
         CurrentChannel.TokenExpiry = DateTime.UtcNow.AddSeconds(tokenData.GetProperty("expires_in").GetInt32());
+        _sessionChanged?.Invoke(CurrentChannel);
         return true;
     }
 
@@ -162,6 +173,7 @@ public class YouTubeAuthService
             TokenExpiry = DateTime.UtcNow.AddSeconds(expiresIn)
         };
 
+        _sessionChanged?.Invoke(CurrentChannel);
         return CurrentChannel;
     }
 }