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Single Sign-On Integration in Symfony
3 min readMay 30, 2025
Introduction
Single Sign-On (SSO) streamlines user access across services via one authentication flow. In Symfony, you can integrate any SSO provider by implementing a custom “credentials provider” (Authenticator) that exchanges an authorization code for a token, fetches user info, and issues a Security token.
Why Use a Custom SSO Authenticator?
- Uniform Authentication: Centralized login across apps.
- External Identity Management: Leverage Keycloak, Auth0, Okta, etc.
- Enhanced Security: Benefit from MFA, anomaly detection, key rotation, etc.
Symfony’s Security component (v5.4+) supports a custom Authenticator model — ideal for OAuth2/OpenID Connect flows.
High-Level Flow
- User hits
/login
→ redirects to IdP’s/authorize
withresponse_type=code
. - IdP returns
?code=…
→ yourSsoAuthenticator
exchanges it at/token
. - Receive
access_token
→ query/userinfo
. - Create
Passport
&UserBadge
→ Symfony issues a session token.
flowchart LR
A[Login Form] --> B{Supports?}
B -- yes --> C[Exchange Code at /token]
C --> D[Get User Info]
D --> E[Build Passport → Token]
E -->…