When to build authentication into your B2B SaaS

When it comes to building and launching innovative B2B SaaS products, advanced authentication methods such as SSO often sit in a peculiar position. They're critical to security and enterprise readiness, yet frequently relegated to "we'll deal with it later" status.

The timing of when you implement enterprise-level authentication capabilities can significantly impact your product's development velocity, security posture, and enterprise readiness.

As one developer observed bluntly on Reddit: "Wiring up auth retroactively is insanely annoying, and you will absolutely miss something."

Strategic timing decisions around authentication implementation can make or break scaling efforts.

In this article, we'll explore three distinct scenarios for implementing authentication, incorporating real-world perspectives from founders and developers who've been through these scenarios before.

Scenario 1: Baking advanced authentication into your MVP

Every MVP needs authentication, but to which level do you take it? From simple social logins to passwordless and SSO, your MVP could have varying levels of authentication.

When advanced auth methods make sense

• You're building security-focused products
• You're explicitly targeting enterprise customers from launch

The benefits

Starting with advanced authentication baked into your MVP establishes proper security foundations from the beginning. It prevents the costly and error-prone process of retrofitting security later, establishes appropriate data access patterns from day one, and reduces technical debt related to security systems.

One Redditor captured the essence of this approach:

I think starting with auth is a good idea. If you’re still excited about the app after doing the auth you’ll know it’s an idea really worth pursuing.

Another developer shared their personal journey: "For years I'd come up with an idea, code all the fun parts, then abandoned it when it came time to decipher the Identity docs for the 6th time."

The challenges

The early authentication approach can slow initial development velocity as your small team tackles auth complexity before proving product-market fit. The implementation complexity of enterprise features like SSO can be particularly distracting if you're racing to demonstrate core value.

As one founder put it: "People nowadays spend all their time with Auth0 and Cognito; it adds so much complexity to their application. It's just not worth dealing with it in the beginning.”

Scenario 2: Integrating authentication during core product development

When this approach makes sense

• Your product doesn't immediately serve enterprise customers but has a clear enterprise trajectory
• Your product handles sensitive data, but initial users are limited to something like a beta release

The benefits

This middle-ground approach allows you to focus on core functionality initially while planning for authentication integration as your feature set matures. You can model user permissions alongside feature development.

One developer describes their process: "I tend to start with basic auth configured through the app settings right from the beginning. This doesn't distract too much from what I actually want to build and can easily be swapped out for something more fancy such as an OAuth SSO provider or whatever is necessary."

Another noted that they would bake in the auth “instantly” after developing the app:

Create the app, set up routing, create some components (a login page, admin page, regular page, some dummy ones if needed), then straight into setting up auth with route guards. Doing it later is a massive pain.

The challenges

This approach requires careful architecture planning to avoid major refactoring later. You may need to pause feature development to implement authentication properly, and there's always the risk of security gaps if the implementation isn't thorough.

I've been caught in traps where I've been excited to start a new project, only to spend days/weeks figuring out auth before being able to move onto the interesting parts.

Scenario 3: Adding authentication after core product development

When this approach makes sense

• Product-market fit is highly uncertain
• You're not targeting enterprise customers initially
• You have very limited engineering resources (1-2 person team)

The benefits

This approach offers the fastest path to initial market validation. Your development focus remains entirely on core product functionality, and you can choose authentication solutions based on validated user needs rather than assumptions.

One developer argued for this approach: "IMO if it's a solo project and you don't have an 'auth template' to adopt that you're familiar with, start first with a user model and bolt on an auth provider later."

The real-world wake up call

The "auth comes later" approach can work for initial validation, but it comes with significant enterprise-readiness costs. One founder shared this sobering experience:

We were essentially laughed out of the room when we showed our biggest prospect how we managed users in our legacy product. I felt really smug about my fancy hand-coded user management tooling until about 50% into the presentation when I could see an equivalently-smug look + mild sideways head shaking coming from the customer CTO. Running in-house authentication is literally a joke to many of these orgs.

This founder continued: "Realizing that we might have lost a multi-million dollar customer over an ego trip was a bit of a wake-up call... At a certain point, it's about making money and being able to sleep at night."

Learn more : The Authentication Stack Evolution Playbook

Decision framework: When and how should your SaaS implement enterprise auth?

To determine the right timing and method for your authentication implementation, consider these key factors:

1. Target market alignment

If enterprise customers are in your immediate future, authentication should be a front-loaded concern. As one Redditor noted:

Let's assume your SaaS is B2B and you anticipate having many thousands of users. Based on my experience... you'll want to implement SSO + SCIM. You want to allow your customers to bring their own auth system with them (SSO) and be able to 'sync' their users to your SaaS easily (SCIM).

2. Security requirements vs. Development velocity

Balance your security needs against your development speed. One user shared their "just in time" authentication principle:

1. Use managed auth from day 1
2. Implement bare minimum flows
3. Only add social providers after 50+ signups
4. Never “roll your own authentication” until 10k+ users

They added: "I've wasted 20+ hours on custom auth for products nobody used."

3. Build vs. Buy assessment

Building authentication in-house might seem appealing at first, but many developers strongly advocate against it:

"Building your own Auth system is hard, like very, very hard," one developer emphasized. “I would advise you piggyback of another system until you scale to get a competent security tech team to build this architecture OR consider additional security like SMS confirmation on login?

My personal opinion is that you SHOULD build your own once you’re scaling with the right team behind it.”

Another developer with extensive experience was even more direct: "I've built a bunch of SaaS platforms over the years... and almost without fail the biggest chunk of work (especially when you get to a scale where you need external audits like PCI or ISO) ends up being diagnostics, bugfixing, and eventually replacing your auth mechanism as things evolve and standards change."

4. Risk assessment

Consider both technical and business risks. One founder put it bluntly:

If something goes wrong and one of our customers gets breached, I don't want the investigation to wind up at a line of code in my codebase. That means I have to get involved in legal proceedings. I am completely out of the game of touching end-user passwords or MFA tokens now.

The enterprise authentication roadmap

Based on the real-world experiences shared above and our experience with B2B SaaS companies, here's a pragmatic roadmap:

1. For pre-PMF startups: Use managed authentication from day one, but implement minimal flows. Focus on core product validation.
2. For startups finding PMF: Begin planning your enterprise-grade authentication approach. Start integrating SSO capabilities before enterprise customers demand them.
3. For scaling startups: Implement SCIM and advanced enterprise features like role-based access control and just-in-time provisioning as you target larger customers.
4. For established SaaS vendors: Consider whether your authentication capabilities are a competitive advantage or limitation. Many companies discover they're leaving money on the table with inadequate enterprise readiness.

As one developer succinctly concluded: "Auth is a well-understood problem, but easy to get wrong. Use a canned version from the start. Would you really want to develop a database system from scratch or other important pieces of infrastructure rather than the 'unique' features your application will provide users?"

Whether you choose to build or buy your authentication solution, the timing of when you tackle this challenge matters. The right approach aligns with your growth stage, target market, and available resources—allowing you to focus on what truly differentiates your product while ensuring you don't create authentication debt that comes back to haunt you when enterprise customers come knocking.

For a deeper exploration of the build vs. buy considerations when implementing SSO for your SaaS application, check out our detailed analysis.

Sources:‍

[1] At what stage do you add authentication when developing a new app? Why?

[2] “Successful SaaS founders: How do you handle auth?”

[3] “Running in house authentication for B2B SaaS”

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Building auth too late causes tech debt — start strong with a Free account on Scalekit and get enterprise-ready authentication built in from day one. Unsure when to integrate SSO, SCIM, or advanced features? Book time with our auth experts.

FAQs

Should startups include SSO in their initial MVP phase?

While an MVP needs basic authentication, adding SSO and enterprise ready features depends on your target market. If you are building security focused products or explicitly targeting enterprise customers from launch, baking advanced auth into your MVP establishes a solid security foundation. This prevents the costly and error prone process of retrofitting security later. However, for most pre product market fit startups, it is often better to use managed auth with minimal flows. This allows your team to focus on core product validation while avoiding the technical debt of a poorly implemented custom authentication system.

What risks arise when adding enterprise auth retroactively?

Retrofitting enterprise authentication like SSO or SCIM is notoriously difficult and can lead to significant technical debt. Developers often find that wiring up auth retroactively is annoying and prone to missing critical security gaps. Beyond the technical challenges, lacking advanced auth can lead to lost business opportunities. Enterprise CTOs may view in house or basic user management as a security risk, potentially causing you to lose multi million dollar deals. Strategic timing ensures that your data access patterns are established correctly from day one, maintaining a strong security posture as you scale.

Why should B2B companies buy instead of building auth?

Building your own authentication system is an extremely complex undertaking that often leads to ongoing maintenance burdens. As standards change and you face external audits like PCI or ISO, in house systems frequently require extensive bugfixing and eventual replacement. By purchasing a managed service, you offload the legal and technical risks associated with handling sensitive credentials or MFA tokens. This allows your engineering team to focus on building unique product features that drive revenue, rather than reinventing well understood infrastructure that carries high liability if a breach occurs.

How does agent authentication differ from standard user login?

Agent authentication shifts the focus from human to machine interactions. Unlike standard user logins that rely on sessions or cookies, AI agents often require long lived identities managed through machine to machine protocols or dynamic client registration. As AI agents perform autonomous tasks within B2B environments, ensuring they have granular permissions and verifiable identities becomes critical. Implementing robust agent auth ensures that automated processes follow the same security and compliance standards as human users, preventing unauthorized access to sensitive enterprise data across your SaaS ecosystem.

When should a scaling SaaS implement SCIM provisioning?

You should begin planning for SCIM and advanced provisioning features as you find product market fit and start targeting larger enterprise customers. SCIM allows your customers to sync their internal user directories with your SaaS platform automatically. This reduces administrative overhead for their IT teams and ensures that user access is revoked instantly when an employee leaves the company. Implementing SCIM alongside SSO provides a seamless onboarding experience that enterprises expect. It transforms your authentication stack from a basic requirement into a competitive advantage that appeals to sophisticated buyers and security conscious organizations.

What is the best approach for secure M2M communication?

Secure machine to machine communication typically relies on OAuth 2.0 client credentials flows or specialized API keys. For B2B SaaS architecture, it is essential to provide customers with the ability to manage these credentials securely. Using a managed provider for M2M auth ensures that you follow industry best practices for token validation, rotation, and scoping. This is particularly important for integrated AI apps and MCP servers that need to interact with various backend services without human intervention. Robust M2M security prevents unauthorized service access and ensures that every automated request is authenticated and authorized correctly.

How does Dynamic Client Registration benefit AI applications?

Dynamic Client Registration, or DCR, allows AI applications and agents to register themselves with an authorization server programmatically. This is highly beneficial in modern B2B architectures where agents are spun up on demand to perform specific tasks. Instead of manually creating credentials for every new instance, DCR automates the onboarding of these agents while maintaining strict security controls. This approach supports scalability and ensures that each agent has a unique, trackable identity. By implementing DCR, you provide a flexible and secure framework for AI driven automation that meets the rigorous security requirements of enterprise customers.

Why do CISOs prefer managed auth over custom solutions?

CISOs prioritize risk mitigation and compliance, making managed authentication highly attractive. When a company uses a reputable auth provider, the responsibility for securing passwords and MFA tokens rests with experts. In the event of a security investigation, a managed service provides clear audit trails and reduces the legal exposure of the SaaS company. Furthermore, managed solutions typically offer faster paths to SOC2 or ISO compliance. By choosing a specialized provider, engineering leaders can assure their CISOs that the authentication infrastructure is robust, scalable, and follows the latest security standards without draining internal resources.

How should developers secure MCP servers in B2B SaaS?

Securing Model Context Protocol or MCP servers requires a combination of strong authentication and granular authorization. Since these servers often bridge AI models with sensitive enterprise data, they must implement rigorous access controls. Developers should use standard protocols like OAuth to ensure that only authorized agents or users can query the server. Additionally, implementing audit logging for every request helps in maintaining transparency and compliance. By integrating MCP servers into a centralized authentication framework, you ensure that AI driven data access remains secure and consistent with the broader security policies of the enterprise environment.