Single Sign-On Explained: What It Is and Why Your Business Needs It in 2025

Your team starts the day by logging into email. Then Slack. Then the project management tool. Then the CRM. Then the invoicing platform. Then the custom internal system that someone built three years ago.

That's potentially seven separate logins. Seven passwords to remember, reset, and change when a team member leaves. Seven attack surfaces for phishing and credential stuffing.

Single Sign-On (SSO) fixes this. And in 2025, it's accessible to businesses of any size.

What Is Single Sign-On?

SSO is an authentication mechanism that allows a user to log in once — with a single set of credentials — and then access multiple applications without logging in again for each one.

You've experienced consumer SSO when you click "Sign in with Google" on a third-party website. You authenticate with Google, and Google tells the other service "yes, this person is who they say they are." You never gave the third-party service your Google password.

Enterprise SSO works on the same principle but within an organisation:

1. You log in once to your Identity Provider (IdP) — commonly Microsoft Entra ID, Google Workspace, or Okta
2. Your IdP issues a cryptographic token proving your identity
3. Any application that trusts your IdP accepts that token without asking for another password
4. When you finish work and log out, you're logged out of everything simultaneously

The Core Protocols

Under the hood, most SSO implementations use one of two protocols:

SAML 2.0 (Security Assertion Markup Language)

The older, enterprise-standard protocol. XML-based. Used extensively by older enterprise software and anything that needs to integrate with legacy systems. If your company uses Salesforce, ServiceNow, or similar — SAML is probably involved.

OpenID Connect (OIDC)

Built on top of OAuth 2.0. Modern, JSON-based, and designed for web and mobile applications. This is what "Sign in with Google" and "Sign in with Microsoft" use. If you're building a new application, OIDC is the right choice.

The difference matters mainly to developers implementing SSO. As a user, the experience is identical: one login, access to everything.

The Business Case

Security improvement

Password reuse is endemic. When employees use the same password across personal and work accounts (and statistically, 65% do), a breach of any one of those personal services is a potential breach of your business systems.

SSO means employees don't need to create and remember passwords for each application — their identity is managed centrally. When an employee leaves, one deactivation in the IdP immediately revokes access to every connected application.

That's not a minor convenience. That's an entire category of security risk eliminated.

Productivity gains

Research by Forrester found that employees waste an average of 10.9 minutes per week dealing with password resets alone. Across a 20-person team, that's over 188 hours per year spent on something that SSO makes unnecessary.

Beyond resets, the cognitive overhead of managing multiple credentials is measurable. Logging in repeatedly throughout the day creates friction that fragments focus.

Compliance alignment

If your business needs to comply with ISO 27001, Cyber Essentials Plus, or GDPR's access control requirements, centralised identity management through SSO is a significant help. You have a single, auditable source of truth for who has access to what.

SSO for Small Businesses: Microsoft 365

If your business already pays for Microsoft 365, you have SSO infrastructure available to you right now through Microsoft Entra ID (included in all business plans).

Apps you can connect to Entra ID SSO — often in minutes:

• Salesforce
• Slack
• Zoom
• Dropbox
• DocuSign
• GitHub
• Thousands more via the Entra App Gallery

The setup for most gallery applications is under 30 minutes and requires no coding. You configure the app in the Entra portal, assign the relevant users or groups, and they can log in via their Microsoft credentials.

For custom internal applications, integrating OIDC/MSAL (Microsoft Authentication Library) is a day's development work for a competent developer.

SSO for Custom Applications

If you're commissioning a custom web application — an internal tool, a client portal, a custom CRM — requesting SSO support from day one is worth the effort.

A well-implemented OIDC integration means:

• Users log in with credentials they already know
• The application never stores passwords (the IdP handles that)
• MFA policies from the IdP apply automatically — no need to implement MFA separately in the app
• Revoking access is instant when an employee leaves

The alternative — a separate username and password per application — means your developer has to build a full authentication system, including password reset flows, hashing, storage, and MFA. That's weeks of work for something that should be a few hours of integration.

Common Misconceptions

False. Microsoft Entra ID is included in Microsoft 365 Business Basic at £4.60/user/month. If you already pay for Microsoft 365, you already own the infrastructure.

This is why SSO implementations pair with MFA and risk-based authentication. One compromised password is actually harder to exploit when MFA is mandatory and AI monitors login patterns for anomalies.

For common SaaS apps against Entra ID or Google Workspace, setup is guided, documented, and often takes under an hour.

Where to Start

1. Audit your current applications — list every tool your team uses and whether it supports SAML or OIDC
2. Choose an Identity Provider — if you're on Microsoft 365, Entra ID is already there. If you're on Google Workspace, Google Identity is the equivalent.
3. Start with the highest-risk apps — anything that holds customer data or financial information
4. Enable MFA on your IdP — there is no reason not to do this immediately
5. Build new apps with SSO from day one — never commission a custom application that doesn't support it

SSO isn't a luxury. For any business with more than a handful of staff and more than a handful of tools, it's the baseline of sensible security hygiene.

Talk to us about SSO integration for your custom applications.