add refresh tokens

api/src/Models/RefreshToken.cs

@@ -0,0 +1,21 @@
+
+// a refresh token's purpose is to authenticate user's without logging in
+public class RefreshToken {
+
+    public int Id { get; set; }
+
+    public string Token { get; set; } = "";
+    
+    public string UserId { get; set; } = ""; // in EF Identity the IdentityUser's id is a GUID string (32 hex digits)
+
+    public DateTime CreatedAt { get; set; }
+    public DateTime ExpiresAt { get; set; }
+    public bool IsRevoked { get; set; }
+
+}
+
+public class TokenDto {
+
+    public string RefreshToken { get; set; } = "";
+
+}