Verifying the Tokens (WSE method) in WCF

My current method to verify the username and password (Tokens) in WSE is as follows:

public override void VerifyToken(SecurityToken token1)
{
    if (token1 is UsernameToken)
    {
        string u1 = (token1 as UsernameToken).Username;
        string p1 = (token1 as UsernameToken).Password;

        // see if this user is already authenticated
        UsernameToken token2 = TokenCache[u1] as UsernameToken;
        if ((token2 != null) && token2.IsCurrent && (token2.Password == p1))
        {
            // less than 30s?
            if ((DateTime.Now - token2.Created) < TimeSpan.FromSeconds(30))
                return;
            else
                // no - remove from cache
                RemoveFromCache(token1);
        }

        // not cached, so actually check
        // NB Two or more requests for same user at about same time may all fail test above
        // and thus all will call ValidateUser.  But then they will all call CacheSecurityToken below,
        // which is OK - the last one wins.
        if (Membership.ValidateUser(u1, p1))
        {
            Cache(token1);
            return;
        }

        // not authenticated
        throw new Exception("Authentication failed for " + u1);
    }

Any idea how can I make changes in WCF? I Have used Microsoft.Web.Service3 WSE assembly - don't want to use that. Want to get rid of UsernameToken from my entire solution.

I have managed verify my security credentials on each webservice call. I have used Directory key-value pair to cache the credentials - if anyone looking for the similar, it would help.

public class SecurityManager : UserNamePasswordValidator
{
    //cacheCredentials stores username and password
    static Dictionary<string, string> cacheCredentials = new Dictionary<string, string>();
    //cacheTimes stores username and time that username added to dictionary.
    static Dictionary<string, DateTime> cacheTimes = new Dictionary<string, DateTime>();

    public override void Validate(string userName, string password)
    {
        if (userName == null || password == null)
        {
            throw new ArgumentNullException();
        }
        if (cacheCredentials.ContainsKey(userName))
        {
            if ((cacheCredentials[userName] == password) && ((DateTime.Now - cacheTimes[userName]) < TimeSpan.FromSeconds(30)))// &&  timespan < 30 sec - TODO
                return;

            cacheCredentials.Remove(userName);
            cacheTimes.Remove(userName);
        }
        if (Membership.ValidateUser(userName, password))
        {
            //cache usename(key) and password(value)
            cacheCredentials.Add(userName, password);
            //cache username(key), time that username added to dictionary 
            cacheTimes.Add(userName, DateTime.Now);
            return;
        }
        throw new FaultException("Authentication failed for the user");       
    }
}