Do I need to rewrite my login flow to add SSO?

Usually, no — you typically don’t need to rewrite your whole login flow to add SSO.

What you usually do is add a new authentication path alongside your existing username/password login:

• User clicks “Sign in with Google / Microsoft / Okta / etc.”
• Your app redirects to the identity provider
• The provider authenticates the user
• Your app receives an auth response
• You map that external identity to a local user/session in your system

When you don’t need a rewrite

You can often keep your current login flow if:

• You already have session handling in place
• Your app can support multiple auth methods
• You can introduce OAuth/OIDC or SAML as an additional option
• Your user records can be linked to external identities

When you might need significant changes

You may need a bigger refactor if:

• Your auth logic is tightly coupled to passwords only
• You have a homegrown auth system with no abstraction for providers
• You need enterprise SSO with SAML, SCIM provisioning, MFA policies, etc.
• Your app assumes every user has a local password
• You need to support account linking across multiple identity providers

Common implementation patterns

1. Keep local login + add SSO buttons

   • Best if you want gradual adoption

2. Use an auth broker/provider

   • Examples: Auth0, Okta, Azure AD B2C, Cognito, Clerk, Firebase Auth
   • This can reduce custom work a lot

3. Implement OIDC/SAML directly

   • More control, more work
   • Usually worth it only if you have specific needs

A good way to think about it

You’re usually not rewriting “login” — you’re abstracting identity so your app can trust multiple ways of proving who the user is.

If you want, I can help you assess your current setup and tell you whether adding SSO would be a small integration or a major refactor.