first commit

services/csharp/lib/ISequenceStore.cs

@@ -0,0 +1,8 @@
+namespace SequenceAuth.Lib;
+
+public interface ISequenceStore
+{
+    Task<Option<SequenceData>> GetSequenceAsync(string sequenceId);
+    Task<StoreOutcome> SaveSequenceAsync(string sequenceId, SequenceData data);
+    Task<StoreOutcome> InvalidateUserSessionsAsync(string userId);
+}