We're a growing startup and need a simple solution for Single Sign-On (SSO) and Multi-Factor Authentication (MFA) to secure our apps. Where should I start?

For a growing startup, I’d start by buying rather than building your own identity system. The core architecture is:

Your apps → Identity Provider (IdP) → SSO + MFA

The IdP handles login, MFA, session management, password policies, and—when needed—federation with customers’ identity systems.

1. Decide what kind of SSO you actually need

There are two common scenarios:

• Workforce SSO: Your employees sign into Slack, GitHub, AWS, internal apps, etc. Look at Microsoft Entra ID, Okta, or similar workforce identity platforms.
• Customer/application SSO: Your customers sign into your SaaS product. Look at Auth0/Okta Customer Identity, WorkOS, Clerk, or similar developer-focused CIAM platforms.

If you're primarily securing your own employees and internal apps, start with a workforce IdP. If you're building a SaaS product where your customers need to authenticate, the second category is usually the better fit.

2. Require MFA, preferably phishing-resistant MFA

At minimum, support an authenticator such as an authenticator app or security key. For higher-security environments, prioritize passkeys/WebAuthn/FIDO2, which provide phishing resistance. NIST's current Digital Identity Guidelines specifically distinguish phishing-resistant cryptographic authentication from manually entered OTP codes.NIST Pages+1

A sensible startup policy is:

• MFA required for employees.
• Passkeys/security keys encouraged or required for administrators.
• Recovery codes and a well-controlled account-recovery process.
• Avoid relying exclusively on SMS for MFA.
• Require reauthentication for particularly sensitive actions.

3. Use standard protocols

For your applications, favor:

• OpenID Connect (OIDC) for modern application authentication.
• SAML 2.0 when integrating with enterprise customers' existing identity providers.
• SCIM later if you need automated user provisioning/deprovisioning.

Don't implement the cryptography or authentication protocol yourself. Let the identity provider's SDK and standards handle it.

4. A practical startup rollout

I'd implement it in roughly this order:

1. Choose one IdP and make it the source of truth for employee identities.
2. Turn on MFA for everyone, starting with administrators.
3. Integrate your highest-risk applications first.
4. Put your own apps behind OIDC.
5. Establish joiner/mover/leaver processes—especially automatic disabling when someone leaves.
6. Keep emergency/break-glass administrator accounts tightly controlled.
7. Add logging and alerts for suspicious authentication activity.
8. Once enterprise customers request it, add SAML SSO and SCIM.

For example, Microsoft documents Conditional Access as a way to deploy and tailor MFA policies across applications.Microsoft Learn

What I'd evaluate before choosing a vendor

Don't just compare the headline price. Check:

If you tell me whether you're securing your employees' internal tools or adding SSO/MFA to a SaaS product for your customers, I can narrow this down to a few concrete architectures and vendors.

For a growing startup, I’d avoid building authentication yourself unless identity is core to your product. Start with a managed identity provider (IdP) and integrate your apps with standard protocols.

A simple architecture

Your apps → Identity provider → SSO + MFA

Look for a provider that gives you:

• OIDC/OAuth 2.0 for modern web/mobile apps.
• SAML 2.0 when enterprise customers need SSO.
• MFA, preferably with passkeys/WebAuthn and authenticator apps.
• User lifecycle management — invite, deactivate, reset, recovery.
• Admin controls — enforce MFA, sessions, groups/roles.
• Audit logs and alerts.
• SCIM provisioning if you're selling B2B and expect larger customers.

SSO means users authenticate once with the identity provider and can then access assigned applications without repeatedly signing in.Microsoft Learn

What I'd implement first

1. Pick one IdP rather than creating your own authentication system.
2. Make the IdP the source of truth for authentication.
3. Integrate your application using OIDC.
4. Require MFA for your company's employees/admins immediately.
5. Offer MFA to customers, initially with authenticator apps and preferably passkeys.
6. Add SAML SSO + SCIM when enterprise customers start requesting them.
7. Keep authorization (what a user can do inside your app) separate from authentication (who they are).

For security, don't treat every MFA method as equivalent. NIST's current SP 800-63B-4 recommends making a phishing-resistant option available at its AAL2 level and explains that manually entered OTP codes aren't considered phishing-resistant.NIST Computer Security Resource Center+1

Choosing the provider

For a startup, I'd evaluate managed options such as:

• Auth0 — developer-oriented customer authentication.
• WorkOS — particularly oriented toward B2B/enterprise SSO and directory provisioning.
• Microsoft Entra ID — attractive if your organization is already heavily invested in Microsoft.
• Okta — established workforce/customer identity platform.

The important question isn't simply "which provider is best"; it's whether you need workforce identity, customer identity, or both.

If you tell me (a) your tech stack, (b) roughly how many employees/users you have, and (c) whether this is B2B SaaS or consumer-facing, I can lay out a concrete architecture and shortlist the appropriate options, including likely cost/complexity tradeoffs.

For a growing startup, I’d avoid building SSO/MFA yourself. Use a managed identity provider (IdP) and make it the central authentication layer for your apps.

A simple starting architecture

Users
  ↓
Identity Provider (IdP)
  ├── SSO
  ├── MFA / passkeys
  ├── User lifecycle
  └── Security policies
  ↓
Your apps
  ├── OIDC / OAuth 2.0
  └── SAML for enterprise customers

For new applications, prefer OpenID Connect (OIDC) / OAuth 2.0. SAML is still important when you need to integrate with enterprise customers' existing identity systems. Microsoft similarly recommends OIDC/OAuth for applications that support it and SAML for existing apps that don't.Microsoft Learn+1

Which provider should you consider?

• Microsoft Entra ID — particularly attractive if your company already uses Microsoft 365. It provides centralized SSO, MFA, Conditional Access, and support for both OIDC and SAML.Microsoft Learn+1
• Okta — a strong choice when you want a dedicated workforce identity platform and expect lots of enterprise integrations.
• Clerk — worth considering if you're primarily a software company and want authentication tightly integrated into your application. Its current offering supports enterprise SSO through SAML/OIDC and can add MFA on top of an enterprise IdP.Clerk
• Auth0 — another common developer-oriented option when you want authentication functionality embedded directly into your products.

My rule of thumb

Internal workforce SSO: start with Entra ID or Okta.

Authentication for your SaaS product's customers: look at Clerk, Auth0, or a similar developer-focused identity platform.

The distinction matters because your employees signing into your company's apps and your customers signing into your product are somewhat different identity problems.

What I'd implement first

1. Pick one IdP rather than integrating every provider individually.
2. Put your first application behind OIDC authorization-code flow.
3. Turn on MFA for administrators immediately, preferably phishing-resistant authentication/passkeys where practical. Entra, for example, supports FIDO2/passkeys and risk-based MFA.Microsoft Learn
4. Establish groups/roles in the IdP rather than hard-coding individual users in applications.
5. Add automated provisioning/deprovisioning as you grow. SCIM can synchronize account creation, updates, and removal between an IdP and your application.Clerk
6. For enterprise customers, add SAML/OIDC federation so customers can connect their own Entra/Okta/Google identity system.
7. Have a documented break-glass administrator account and recovery process before enforcing MFA everywhere.

One important design decision

Don't make your applications responsible for MFA.

Your app should essentially say:

"Authenticate this user and tell me who they are." The identity provider handles the password/passkey, MFA, conditional-access policies, suspicious-login detection, recovery, etc. Your application validates the resulting tokens and makes authorization decisions such as "is this person an admin?"

That separation keeps your security architecture considerably simpler.

If you tell me (a) whether SSO is for your employees or for customers of your SaaS, (b) your tech stack, and (c) roughly how many users you have, I can recommend a specific setup and give you a concrete implementation plan.

For a growing startup, the simplest path is usually not to build authentication yourself. Start with a managed Identity Provider (IdP) that gives you SSO, MFA, user management, and security policies as a service. SSO is typically built around standards like OpenID Connect (OIDC) for modern apps and SAML for many enterprise integrations.Microsoft Learn+1

1. Clarify what you need to protect

Make a quick inventory:

• Internal tools

• Admin dashboards

• Developer tools

• Cloud consoles

• HR/finance apps

• Customer-facing apps

• SaaS product login

• Customer portals

• APIs and mobile apps

• Enterprise customer requirements

• “Login with our company identity provider”

• SAML SSO

• SCIM user provisioning

• Audit logs

Your choice depends heavily on whether you need workforce identity (employees) or customer identity (your users).

2. Pick an identity platform

Common startup-friendly options:

• auth0.com — good for customer-facing applications and developer-focused teams; supports SSO patterns using OIDC, SAML, and other identity connections.Auth0
• okta.com — commonly used for employee access management.
• microsoft.com — a strong choice if your organization already uses Microsoft 365.
• cloud.google.com — useful for teams already centered around Google Workspace.

For many startups:

• Employees → Okta / Entra ID / Google Cloud Identity
• Customers → Auth0 or another customer identity platform

3. Use modern authentication standards

For new applications:

• Prefer OIDC + OAuth 2.0 for web apps, mobile apps, and APIs.
• Support SAML when enterprise customers require it.Microsoft Learn

Avoid:

• Rolling your own password storage
• Creating your own MFA system
• Passing passwords between your services

4. Enable MFA with strong defaults

A good baseline:

• Require MFA for: - Admins
• Developers
• Finance users
• Anyone with production access

Prefer:

1. Passkeys / hardware security keys
2. Authenticator apps (TOTP or push)
3. SMS only as a fallback

Also set up:

• Recovery codes
• Device management
• Login alerts
• Session expiration policies

5. Design your app integration

A typical flow:

1. User visits your app.
2. App redirects them to your IdP.
3. IdP performs login + MFA.
4. IdP returns a signed token.
5. Your app validates the token and creates a session.

Your app should manage authorization separately:

• Authentication = “Who is this user?”
• Authorization = “What can this user do?”

Example:

• User logs in successfully.
• Your system checks whether they are an admin, manager, or regular user.

6. Build the basics before enterprise features

A practical startup rollout:

Phase 1 — Foundation

• Choose IdP
• Integrate OIDC login
• Enable MFA
• Centralize employee access

Phase 2 — Security controls

• Role-based access control (RBAC)
• Audit logs
• Automated employee onboarding/offboarding

Phase 3 — Enterprise readiness

• Customer SAML SSO
• SCIM provisioning
• Domain verification
• Advanced reporting

7. Avoid common mistakes

• ❌ Building authentication in every app separately
• ❌ Letting production admins use passwords only
• ❌ Storing unnecessary identity data
• ❌ Mixing login logic with business permissions
• ❌ Waiting until enterprise customers demand SSO before designing for it

If you are a typical early-stage SaaS startup, a reasonable starting architecture is:

Customer apps: Auth0 (or similar) + OIDC + MFA Employee access: Okta/Entra ID/Google Cloud Identity + enforced MFA Authorization: Your own RBAC layer backed by your application database

If you share whether you mean employee SSO, customer login, or both, and what your stack is (AWS/GCP/Azure, React, Django, Node, etc.), I can suggest a more specific setup.

For a growing startup, I’d avoid building SSO/MFA yourself. Start with a managed identity provider (IdP) and make it the central authentication layer for your apps.

A simple starting architecture

Your apps → Identity Provider → SSO + MFA

The main options I’d evaluate are:

• Microsoft Entra ID — especially attractive if your company already uses Microsoft 365. It supports SSO through standards such as OpenID Connect (OIDC) and SAML, plus centralized MFA and access policies.Microsoft Learn+1
• Okta — a strong dedicated identity platform if you want identity management to be vendor-neutral.
• Auth0 — worth considering if the primary problem is adding authentication to your own customer-facing SaaS rather than managing employee access.

What I'd implement first

1. Pick one IdP as your source of truth. Don't let each application maintain its own users, passwords, and MFA configuration.
2. Use OIDC for new applications. For a modern web app, use the authorization-code flow with an established SDK/library. Use SAML primarily when integrating with enterprise applications that require it. Microsoft specifically recommends OIDC/OAuth when an application supports it.Microsoft Learn
3. Turn on MFA for everyone. At minimum, require it for administrators and privileged accounts immediately. MFA adds a second barrier if a password is compromised.NIST
4. Prefer passkeys/FIDO2 over SMS when possible. SMS and some OTP approaches are vulnerable to phishing; FIDO-based authenticators/passkeys provide much stronger phishing resistance.NIST+1
5. Centralize authorization too. Define groups/roles such as employee, engineering, finance, and admin, then have applications consume those claims rather than inventing separate access systems.
6. Plan for employee lifecycle. When someone joins, changes roles, or leaves, their identity and application access should be managed centrally. This becomes increasingly important as the startup grows.

A pragmatic startup rollout

Week 1: Choose IdP → create tenant → configure your company domain → enable MFA.

Week 2: Integrate your most important internal app using OIDC → pilot with 5–10 users.

Week 3: Migrate remaining internal apps → establish groups/roles → require MFA for admins.

After that: Add automated provisioning/deprovisioning, audit logs, conditional access, and stronger phishing-resistant authentication.

The important architectural decision is not SSO vs. MFA—they solve different problems: SSO centralizes authentication across applications, while MFA strengthens the authentication itself. A managed IdP gives you both in one control plane.Microsoft Learn+1

If you tell me (a) whether these are employee/internal apps or customer-facing apps, (b) your cloud stack, and (c) roughly how many users you have, I can narrow this down to a specific low-complexity architecture and vendor choice.