I work a lot with Oracle and with Oracle-related (from Oracle or third party) tools. It’s my job, since I’m a DBA and also a developer that happens to be using Oracle a lot as a backend-database.
A lot of tools don’t know that Oracle has a feature “operating system authentication”. If you define a user in Oracle as authenticated by the OS (Windows, Unix, whatever), you basically tell Oracle: see if the OS-user trying to login is defined in Oracle, and if so, don’t ask for a password, since the user already supplied that to the OS. Think of it as MS Passport, but in a very simplistic way (but then again, it already exists more than a decade!).
You tell Oracle to login as the OS-user by supplying a slash (“/”) as username-password, basically saying “no-username/no-password”.
Filling in a slash or leaving the username/password fields empty is not recognised by many tools. They just don’t enable the OK or Connect button unless you fill in both fields.
To my surprise, I got this dialog:
when I tried to define a new Oracle connection in Visual Studio .NET using the just released Oracle Developer Tools for VS.NET. WTF?!