Single sign on authentication

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Single Sign-On (SSO) is an authentication process that allows users to access multiple applications with one set of login credentials. This simplifies the user experience and enhances security by centralizing authentication. Here’s how SSO works, step-by-step:

Components of SSO

  1. Identity Provider (IdP): The system that performs the authentication and issues authentication tokens or assertions. Examples include Okta, Azure AD, and OneLogin.
  2. Service Provider (SP): The application or website that the user wants to access.
  3. User: The person who wants to access multiple applications.

Protocols

SSO typically relies on standard protocols like:

  • SAML (Security Assertion Markup Language): Often used in enterprise settings.
  • OAuth/OpenID Connect: Common for web and mobile applications.

How SSO Works (Using SAML as an Example)

Step-by-Step Process

  1. User Accesses the Application:
    • The user tries to access a Service Provider (SP) application.
  2. Redirect to IdP:
    • If the user is not authenticated, the SP redirects the user to the Identity Provider (IdP) for authentication. This is often done via an HTTP redirect to the IdP’s SSO URL.
  3. User Authenticates:
    • The user provides their login credentials (e.g., username and password) to the IdP.
    • The IdP authenticates the user, typically by checking their credentials against a user database or directory (e.g., LDAP, Active Directory).
  4. IdP Issues SAML Assertion:
    • Upon successful authentication, the IdP generates a SAML assertion, which is an XML document containing user authentication and attribute information.
    • This assertion is digitally signed by the IdP to ensure its integrity and authenticity.
  5. Redirect Back to SP:
    • The IdP redirects the user back to the SP with the SAML assertion, usually through the user’s browser. This can be done using an HTTP POST request.
  6. SP Validates the Assertion:
    • The SP receives the SAML assertion and validates the digital signature to ensure it was issued by a trusted IdP.
    • The SP also checks the assertion’s validity (e.g., expiration time, intended audience).
  7. User Authenticated at SP:
    • If the assertion is valid, the SP establishes a session for the user and grants access to the requested resource.
    • The user is now authenticated and can access the application without needing to log in again.
  8. Access to Multiple Applications:
    • Because the user is authenticated by the IdP, they can access other SP applications that trust the same IdP without needing to log in again.
    • The user’s session at the IdP is used to authenticate subsequent access requests to other SPs.

Benefits of SSO

  1. Improved User Experience:
    • Users only need to log in once to access multiple applications, reducing login fatigue.
  2. Enhanced Security:
    • Centralized authentication allows for stronger, more consistent security policies (e.g., multi-factor authentication).
    • Reduced password fatigue decreases the likelihood of poor password practices (e.g., reuse of weak passwords).
  3. Simplified Management:
    • Easier management of user credentials and access controls.
    • Centralized logging and monitoring of authentication events.

Example Flow Using OAuth/OpenID Connect

  1. User Initiates Login: The user accesses a client application and clicks “Login with [IdP]”.
  2. Authorization Request: The client redirects the user to the IdP’s authorization endpoint.
  3. User Authenticates: The user logs in at the IdP.
  4. Authorization Response: The IdP sends an authorization code back to the client.
  5. Token Exchange: The client exchanges the authorization code for an access token and ID token.
  6. Access Granted: The client uses the ID token to authenticate the user and provide access.

Conclusion

SSO streamlines the login process by allowing users to authenticate once and gain access to multiple applications. By leveraging protocols like SAML and OAuth/OpenID Connect, SSO provides a secure and efficient way to manage authentication across diverse systems and applications.

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