<system.serviceModel>
<bindings>
      <wsHttpBinding>
        <binding name="UserNameTransportSecurity" >
          <security mode="TransportWithMessageCredential">
            <transport clientCredentialType="None" />
            <message clientCredentialType="UserName" algorithmSuite="Default"/>
          </security>
        </binding>
      </wsHttpBinding>


<behaviors>
      <serviceBehaviors>
        <behavior name="UserNameAuthentication">
          <serviceCredentials>
            <userNameAuthentication
                userNamePasswordValidationMode="Custom"
                customUserNamePasswordValidatorType="Namespace.CredentialValidator, Assembly"/>
          </serviceCredentials>
        </behavior>
      </serviceBehaviors>
    </behaviors>

<services>
      <service name="Namespace.Service" behaviorConfiguration="UserNameAuthentication">
        <endpoint binding="wsHttpBinding" bindingConfiguration="UserNameTransportSecurity"
          contract="Namespace.IService" />
        <endpoint address="mex" binding="mexHttpsBinding" contract="IMetadataExchange" name="MetadataBinding" />
      </service>
    </services>

public class CredentialValidator : UserNamePasswordValidator
    {
        public override void Validate(string userName, string password)
        {
            if(userName != "test " || password != "test")

            try
            {
                using (var connection = new SqlConnection(s.ToString()))
                {
                    connection.Open();
                }
            }
            catch (SqlException)
            {
                throw new SecurityTokenException("Invalid Username or Password.");
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
    }