single sign-on for existing app

Sure — if you want to add single sign-on (SSO) to an existing app, the best approach depends on:

1. What kind of app it is

   • Web app
   • Mobile app
   • Desktop app
   • API/backend only

2. Who your identity provider should be

   • Microsoft Entra ID (Azure AD)
   • Google Workspace
   • Okta
   • Auth0
   • OneLogin
   • Your own IdP

3. Which protocol you want to use

   • OpenID Connect (OIDC): usually best for modern apps
   • SAML 2.0: common in enterprise/legacy environments
   • OAuth 2.0: for authorization, often paired with OIDC for login

Recommended default

For most existing modern apps, use:

• OpenID Connect for login
• Authorization Code Flow with PKCE
• JWT access tokens / ID tokens
• Centralized logout if needed

Typical integration steps

1. Choose an identity provider
2. Register your app with the IdP
3. Configure redirect/callback URLs
4. Implement the login flow
   • redirect user to IdP
   • receive authorization code
   • exchange code for tokens
5. Validate tokens
   • signature
   • issuer
   • audience
   • expiration
6. Create/update local user session
7. Map IdP user claims to app roles/permissions
8. Handle logout and session expiration

Common patterns for existing apps

If your app already has username/password login

You can:

• keep local login temporarily
• add SSO as another login option
• gradually migrate users to SSO

If your app uses server-side sessions

• SSO authenticates the user
• your app creates its own session cookie after successful login

If your app is a SPA

• use OIDC with PKCE
• avoid storing tokens in localStorage if possible
• prefer secure cookies or in-memory token handling

Important considerations

• User provisioning: do you want just-in-time user creation or pre-provisioned accounts?
• Role mapping: how will app roles be assigned from SSO groups/claims?
• Multi-tenant support: one org or many orgs?
• Security: enforce HTTPS, secure cookies, CSRF protection, token validation
• Fallback login: what happens if SSO is unavailable?

If you want to implement this quickly

A common architecture is:

• IdP handles authentication
• App trusts OIDC/SAML response
• App maintains its own session
• App uses claims/groups to authorize access

If you want, I can help you with one of these next:

1. A step-by-step SSO integration plan
2. SSO architecture for your specific app
3. Example code in Node.js / Python / Java / .NET / PHP
4. Choosing between SAML and OIDC