grant codeBase "file:/install_dir/lib/51/-" {
   permission javax.security.auth.AuthPermission
      "createLoginContext.DDTEK-JDBC";
   permission javax.security.auth.AuthPermission "doAs";
   permission javax.security.auth.kerberos.ServicePermission 
      "krbtgt/your_realm@your_realm", "initiate";
   permission javax.security.auth.kerberos.ServicePermission 
      "MSSQLSvc/db_hostname:SQLServer_port@your_realm", "initiate";
};

where:

install_dir
is the product installation directory.
your_realm
is the Kerberos realm (or Windows Domain) to which the database host machine belongs.
db_hostname
is the host name of the machine running the database.
SQLServer_port
is the TCP/IP port on which the Microsoft SQL Server instance is listening.