Impersonate using the ActOnBehalfOf privilege

https://msdn.microsoft.com/en-us/library/gg309629.aspx

// Connect to the Organization service. 
// The using statement ensures that the service proxy will be properly disposed.
using (_serviceProxy = new OrganizationServiceProxy(serverConfig.OrganizationUri, serverConfig.HomeRealmUri,serverConfig.Credentials, serverConfig.DeviceCredentials))
{
    // This statement is required to enable early-bound type support.
    _serviceProxy.EnableProxyTypes();

    CreateRequiredRecords();

    // Retrieve the system user ID of the user to impersonate.
    OrganizationServiceContext orgContext = new OrganizationServiceContext(_serviceProxy);
    _userId = (from user in orgContext.CreateQuery<SystemUser>()
              where user.FullName == "Kevin Cook"
              select user.SystemUserId.Value).FirstOrDefault();

    // To impersonate another user, set the OrganizationServiceProxy.CallerId
    // property to the ID of the other user.
    _serviceProxy.CallerId = _userId;

    // Instantiate an account object.
    // See the Entity Metadata topic in the SDK documentation to determine 
    // which attributes must be set for each entity.
    Account account = new Account { Name = "Fourth Coffee" };

    // Create an account record named Fourth Coffee.
    _accountId = _serviceProxy.Create(account);
    Console.Write("{0} {1} created, ", account.LogicalName, account.Name