I'm having the same problem as you. There is practically no Sustainsys authentication documentation for ASP.NET Web Forms. Did you manage to solve it? If so, could you post it here?
Thanks
Reasons:
Blacklisted phrase (0.5): Thanks
Blacklisted phrase (1): I'm having the same problem
RegEx Blacklisted phrase (2.5): could you post
RegEx Blacklisted phrase (3): Did you manage to solve it