It is best to assume you would need to login each time you open your browser off-campus. The library's resources are authenticated through Vanguard SSO (single sign-on). If you are off-campus, you will be prompted for your Vanguard email address and password. Once you have logged in, you can use different databases without being prompted for your username and password, but if you close your browser, you may need to log in again (depending on how you have your browser's security settings configured).
