When you first try and use a web app with stored credentials (SSO), you will be prompted to install the ClassLink Browser Extension. You can tell what apps use this by the "Key" icon in the top right corner.
When the app launches it will prompt you for the extension installation. Click on "Install Extension".
You will be redirected to the chrome web store and must be logged in to your Google account. Click on the "Add to Chrome" button.
On the notification pop-up, you want to click "Add extension".
After installing the extension you will want to return to the ClassLink dashboard and launch the web app again. You should be prompted to enter your credentials for the first time. If you prefer not to store your credentials you can select the "Skip" button.