CircleBack now allows for single sign-on (SSO), using Exchange, Microsoft, or Google accounts.
When you first launch the app, press the "Get Started" button. The resulting screen will provide options for signing in with the account of your choice:
Tap to choose the account type you wish to use*. Once you have chosen the account type, you will be presented with the accounts of that type that you have on your device. For example, if you choose Google, you can then choose from the Google accounts that are on your device.
Select the account you wish to use and CircleBack will sign you in using that account.
If you don't wish to use SSO, press "Create Account with Email" on the screen pictured above. When prompted, enter the email address you wish to use to create your CircleBack account. Following that, create your CircleBack password and follow the on-boarding instructions.