It looks like your question pertains to authenticating to Denodo using Kerberos and version 3.x of NPGSQL.
I have noticed that there are a few conditions to be met for that purpose and one of them is
* The application has to use the version 2.2.7 version of the Npgsql provider.
You can find this information for Denodo version 7.0 in the [Using Kerberos Authentication](https://community.denodo.com/docs/html/browse/7.0/vdp/developer/access_through_an_ado.net_data_provider/using_kerberos_authentication/using_kerberos_authentication#using-kerberos-authentication) section of the Virtual Dataport Developer Guide.
The requirement is the same for Denodo version 8.0, please refer to this [link](https://community.denodo.com/docs/html/browse/8.0/vdp/developer/access_through_an_ado.net_data_provider/using_kerberos_authentication/using_kerberos_authentication).
If you have access to Denodo Support, please open a case to investigate this further.
I hope this helps.