Any reputable method of storing passwords will work, as long as your site is protected by SSL.
All client tools rely on the TeamForge SOAP API for authentication, and therefore use whatever authentication method TeamForge is using.
Many standalone client tools are able to cache a copy of the user's credentials to make it easier for them to access the site. The CollabNet Eclipse Desktop stores passwords in the encrypted Java keystore, and the CollabNet Windows clients use the Windows keystore.
CollabNet's Subversion clients and other Subversion clients, such as Tortoise and Subclipse, are also able to store user credentials. While CollabNet has no control over how third-party tools store such credentials, it our experience that the mainstream tools all use an appropriate keystore for secure storage of user credentials. CollabNet recommends that customers independently verify the storage methods of those tools and set a policy appropriate with their own security guidelines.
Subversion users on Linux systems have the option to use the Gnome keyring to securely store user credentials. CollabNet recommends that customers set their own policy for how their users should use the Linux Subversion client.