CRM Custom Workflow login user to same SharePoint Login User

Hello,

I am created one custom workflow activity code and upload the document template to the SharePoint site library with the document management mapping from CRM but I am facing issue while I am use System.Net.CredentialCache.DefaultCredentials for SharePoint Login it will not allowed to login with same CRM user.(401 authentication issue). also same user are in CRM and SharePoint.

Thanks