sql server - Impersonation failing for database connection -

i have sl4 app uses wcf communicate backend sql server 2008 database. 1 of wcf services needs connect database dedicated system account due database permissions required stored procedure called. have attempted implement solution using impersonation within service code e.g.

int result = logonuser(username, domain, password,     logon32_logon_network, logon32_provider_default, out _token);  if (result > 0) {     impersonateloggedonuser(_token);     //code here call nhibernate data access code } 

my connection string service is:

<add name="myconnection" connectionstring="data source=servername\instance;initial catalog=mydatabase;integrated security=sspi" providername="system.data.sqlclient"/> 

however, data access routine still failing following message:

login failed user 'nt authority\anonymous logon'.

the impersonation being ignored in database connection. ideas?

change logon32_logon_network logon32_logon_network_cleartext in call logonuser.

this caches logon credentials in local security provider, should enable successful sspi handshake sql server.