Initial commit

Services/Auth/ITokenRefreshService.cs

@@ -0,0 +1,17 @@
+namespace SharepointToolbox.Web.Services.Auth;
+
+public interface ITokenRefreshService
+{
+    /// <summary>
+    /// Exchanges a refresh token for a new access token using the public-client flow (no secret).
+    /// ClientId is per-tenant (from TenantProfile) — no global secret required.
+    /// </summary>
+    Task<TokenRefreshResult> RefreshAsync(string refreshToken, string tenantId, string clientId, string scope);
+}
+
+public class TokenRefreshResult
+{
+    public string AccessToken { get; set; } = string.Empty;
+    public string RefreshToken { get; set; } = string.Empty;
+    public DateTimeOffset ExpiresAt { get; set; }
+}