Authentication for your SaaS product is the one bit of infrastructure almost every founder underestimates. It looks like a weekend job. Login form, password field, a session cookie, done. Then you actually sit down to build it properly and discover you have signed up for password resets, email verification, multi factor authentication, session management, social login, single sign on for your bigger customers, and a genuinely terrifying amount of security surface area.
I have built authentication from scratch and I have bought it in, on different products, for good reasons each time. There is no universally correct answer here, whatever a vendor's marketing page tells you. There is only the right answer for where your product and your business actually are right now.
Why authentication feels simple and is not
The login form itself is genuinely easy. Hash a password, check it against the database, set a cookie or issue a token. A junior developer can build that part in an afternoon. The trouble is that a login form is not authentication, it is about five percent of authentication.
The other ninety five percent is password reset flows that do not leak whether an account exists, email verification that does not get caught in spam filters, brute force protection, session revocation when a device is lost, audit logging for who logged in from where, and eventually multi factor authentication because a customer's compliance team will demand it. Every one of those is a place where a small mistake becomes a security incident, not just a bug.
The case for buying it in
Services like Auth0, Clerk, Azure AD B2C and AWS Cognito exist because this problem is both hard and extremely well understood. Thousands of engineering hours have already gone into getting the edge cases right on your behalf. You are not paying for a login form, you are paying to never have to think about a specific class of security bug again.
What a good identity provider actually saves you
The real saving is not the initial build time, though that helps too. It is every future feature you get for free as your customers grow up. Enterprise customers ask for single sign on with their own identity provider. Someone asks for SCIM provisioning. Someone else needs SOC 2 evidence about how you handle authentication. A decent identity provider has already solved all of this, and you flip a setting rather than build a project.
This matters more the moment you start selling to bigger companies. I wrote about the wider trade offs of paying for infrastructure instead of building it in build versus buy for business owners, and authentication is one of the clearest examples of that argument in practice. It is rarely your competitive advantage, so it rarely deserves your engineering time.
The case for building it yourself
None of that means buying in is always right. There are real reasons to build your own, and they are not just ego or a desire to avoid a monthly bill.
When rolling your own genuinely makes sense
If authentication genuinely is close to your product, build it. A platform selling identity or access management as its actual product cannot outsource the thing it sells. If you have very unusual requirements around data residency, or you are in a regulated sector where customer data cannot leave a specific jurisdiction, some providers make that awkward or expensive.
Cost at real scale is the other honest reason. Most identity providers price per active user, and that model that looks trivial at fifty customers can become a genuinely large line item once you are into the tens of thousands of users. At that point the calculation changes, because you are no longer comparing a subscription to a weekend of work, you are comparing an ongoing five or six figure bill to a proper engineering investment with a real payback period.
What I actually did with CampSuite
With CampSuite I went with ASP.NET Identity underneath our own login flow rather than an external identity provider, mostly because the product is built on .NET already and Identity plugs straight into that stack without introducing a third party dependency into the login path. That decision has held up fine, but it was a deliberate trade off, not a default. I accepted more of the ongoing maintenance burden in exchange for one less external vendor sitting between a customer and getting into the product.
On other projects, including consulting work where the client is a small team without dedicated security expertise, I have pushed hard for buying in. If a team does not have someone whose job is genuinely thinking about session security and credential handling, an external identity provider is doing that thinking for them, and that is worth paying for. I covered the wider version of this argument in how to secure a SaaS application without a security team, and authentication is usually the first thing I point people at.
The questions that actually decide it
Ignore the marketing and ask yourself four things. Is authentication close to what you are actually selling, or is it pure plumbing that gets a customer to the product they came for? Do you have anyone on the team who understands session security properly, or would you be learning it live in production? What does realistic pricing look like at your actual projected user count in two years, not today? And how soon will an enterprise customer ask for single sign on, because that question arrives earlier than most founders expect.
For almost every early stage SaaS product, the honest answers point towards buying in. You do not know yet whether authentication will ever be a differentiator for you, your team is small, and the pricing at your current scale is genuinely trivial next to the cost of your own time. Build the product people are actually paying for instead.
My actual recommendation
Buy in by default. Reach for Clerk or Auth0 if you want the fastest path to something solid, or Azure AD B2C if you are already deep in the Microsoft stack and want it to sit naturally alongside the rest of your infrastructure. Only build your own if authentication is genuinely close to your product, your scale has made the pricing model painful, or you have a data residency requirement that forces your hand.
Whichever way you go, treat the decision as a real architectural choice rather than an afterthought bolted on in week one. It touches almost every other part of a SaaS product eventually, and unpicking a bad early decision here is far more painful than most technical debt. If you want a second opinion on your own setup, this is exactly the kind of decision I help clients think through as part of software development consulting, and it is one of the recurring themes in The 28 Day Startup.
