SOC 2 does not require a formal Single-Sign-On (SSO) solution. As a good security practice, SSO should be used whenever possible across all organization sizes regardless of your team size.

Recommended SSO Solutions: 

• Google Cloud Identity is a great solution for companies already using GSuite. There is a free version that you can deploy to your organization very quickly. 
• Azure Active Directory is a great solution for companies already using Office 365.
• Okta has a more robust platform and is a better fit for larger organizations but will often require an annual contract.
• Many companies will also charge you additional fees for SSO.