If you use K2 SmartForms for Forms technology, then logging in would just be the SQLUM Username and password.

If you want to connect to the K2 server from .NET code, then you are probably looking at using the Workflow Client API or Workflow Management API depending on use case:

https://help.nintex.com/en-US/k2five/devref/current/Content/Runtime/WF-Client/WF-ClientAPI.htm

https://help.nintex.com/en-US/k2five/devref/current/Content/Runtime/WF-Manage/WFManage-Intro.htm

Or calls into the REST endpoints:

https://help.nintex.com/en-US/k2five/devref/current/Content/Runtime/WF-REST-API/WF-REST-API.htm

Workflow Client API and Workflow Management API would use a connection string as below, for example:

https://help.nintex.com/en-US/k2five/devref/current/Content/Concepts/ConnectionStringSamples.htm

Once connected with the SQLUM account, you can impersonate other SQLUM users:

https://help.nintex.com/en-US/k2five/devref/current/Content/Runtime/WF-Client/ImpersonateUser.html

If the user already logs-in via login-in screen in a web application, then you would need to somehow associate this account with the SQLUM account for impersonation.

Thanks for the reply and yes the APIs does help in starting a workflow instance programmatically but in this case i will need to build my own .net form to allow the user to fill the date that is needed to start the process !! 

what is really needed (if this is doable ) is that , how can i call the Form runtime URL from a .NET application after authenticating the user via the Client APIs ( i am using SQLUM ) , i dont want the login screen for the Forms STS to show when i call the form URL via an ifram within that .NET application ( like what happens when you mark a form to allow  anonymous  access , with the way to authenticate the user before that URL call ?)

so in short i need to call the form runtime URL (to start a workflow , without doing a custom form in my .net application ) and be able to authenticate the user  within that .net application code via an API so that when calling the form runtime URL it does not ask for a user/password ( nothing that i am using Froms STS with SQLUM )

Can this be done ?

Hi @TinTex 
Any more advice you can give here?