question

This code works for me, what version of Steamworks are you using?

 public static string GetSteamAuthTicket()
     {
         byte[] ticketBlob = new byte[1024];
         uint ticketSize;
    
         // Retrieve ticket; hTicket should be a field in the class so you can use it to cancel the ticket later
         // When you pass an object, the object can be modified by the callee. This function modifies the byte array you've passed to it.
         HAuthTicket hTicket = SteamUser.GetAuthSessionTicket(ticketBlob, ticketBlob.Length, out ticketSize);
    
         // Resize the buffer to actual length
         Array.Resize(ref ticketBlob, (int)ticketSize);
    
         // Convert bytes to string
         StringBuilder sb = new StringBuilder();
         foreach (byte b in ticketBlob)
         {
             sb.AppendFormat("{0:x2}", b);
         }
    
         return sb.ToString();
     }

The Steamworks SDK adds a new parameter to the GetAuthSessionTicket method called “pIdentityRemote”, As ISteamUser Interface (Steamworks Documentation) (steamgames.com) mentions that “The identity of the remote system that will authenticate the ticket. If it is peer-to-peer then the user steam ID. If it is a service, a string identifier of that service if one if provided.” And our API LoginWithSteam has added a new field called "TicketIsServiceSpecific" which can be enabled to inform steam that the identity string should be validated along with the Steam ticket. As Authentication - Login With Steam - REST API (PlayFab Client) | Microsoft Learn mentions that this field "TicketIsServiceSpecific" expects a true value if the authentication ticket was generated using ISteamUser::GetAuthTicketForWebAPI() and you need to pass our service's identity string, our identity string is "AzurePlayFab". If the authentication ticket was generated using ISteamUser::GetAuthSessionTicket(), then you need to set "TicketIsServiceSpecific" to false, and it expects the ticket without an identity, just as before.