Login Options for Your App: Passwords, Social Login, SSO, MFA and Passkeys Explained
Every app that stores something personal needs a way to let the right person in and keep everyone else out. The choices have multiplied: passwords, "Continue with Google", single sign-on, one-time codes, authenticator apps and passkeys. Each one affects how many people finish signing up, how often accounts get taken over, and how much support work lands on your team.
This guide explains the main login options in plain terms, who expects which, and how to pick a sensible set for a first release. It is written for people planning web and mobile app development who need to make the decision, not write the code.
The five login options in plain terms
A password is a secret the user types. It is familiar and works everywhere, but people reuse passwords across sites and can be tricked into typing them into a fake page. Social login lets someone sign in with an account they already have, such as Google, Apple or Microsoft. Your app never sees a password; the provider confirms who the person is.
Single sign-on (SSO) is the workplace version of the same idea. A company connects your app to its own staff directory, so employees sign in with their work account and lose access automatically when they leave. Multi-factor authentication (MFA) adds a second proof on top of the first, such as a code from an app or a prompt on a phone. A passkey replaces the password altogether with a cryptographic key stored on the user's device, unlocked by a fingerprint, face or device PIN.
These are not competing choices. Most real products combine two or three of them.
Who expects what: consumers and business customers
Consumers want the shortest route in. For a shopping, booking or community app, an email-based sign-up plus one or two social login buttons is usually enough. If you publish an iPhone app, note that Apple's App Store Review Guidelines (section 4.8) require apps that use a third-party or social login for the main account to also offer an equivalent option that limits data collection and lets users keep their email address private, with some exceptions. Sign in with Apple is the usual way to meet that.
Business customers ask different questions. Once you sell to mid-sized or large organizations in the US or UK, their IT or security team will commonly ask whether your product supports SSO with their identity system, whether MFA can be enforced for all their users, and how accounts are removed when staff leave. If you are building a B2B SaaS product, design the user and organization model so SSO can be added per customer later, even if it is not in the first release.
Where passkeys stand today
The FIDO Alliance defines a passkey as an authentication credential based on FIDO standards that can be stored on a phone or computer, or in a hardware security key. Signing in uses the same action that unlocks the device, and the FIDO Alliance states that biometric information stays on the device and that passkeys are supported in all major operating systems and browsers.
The browser side is a settled standard. Web Authentication Level 3, the API that websites use to create and check passkeys, was published as a W3C Recommendation on 25 August 2026. A key property is that each credential is scoped to the site that created it, which is why a look-alike phishing site cannot use it.
There are two kinds. Synced passkeys are copied between a user's devices through a cloud service such as a password manager, so losing a phone does not mean losing access. Device-bound passkeys never leave one device or security key. Passkeys are current technology, not an experiment, but not every user has adopted them, so offer them alongside another method instead of as the only way in.
Multi-factor options are not equally strong
The UK's National Cyber Security Centre ranks MFA types in this order, based on strength, accessibility and usability:
- FIDO2 credentials, which include passkeys and security keys
- Challenge-based authenticator apps, such as a prompt to approve on a phone
- App-based code generators
- Hardware-based code generators
- Message-based methods, such as codes sent by SMS or email
The reasoning matters more than the ranking. Any code a user types can also be typed into a fake site and relayed by an attacker, and approval prompts can be abused by sending requests until a tired user taps yes. The NCSC says message-based methods are only likely to be appropriate when no other method is possible. US guidance points the same way: NIST SP 800-63B-4, written for US federal systems and widely used as a benchmark, says methods that involve manually entering a code are not phishing-resistant and classes verification over the phone network as "restricted".
A weaker second factor still adds protection over a password alone, so treat SMS as a fallback and steer users toward an authenticator app or a passkey.
Build it yourself or use an identity provider
You can build login inside your own application or hand it to an identity provider, a specialist service that runs sign-up, sign-in, MFA, social login and SSO connections for you. Modern frameworks include solid building blocks for password login, sessions and password reset, so building basic authentication yourself is reasonable when requirements are simple and you want full control of the data and the screens.
The balance shifts as requirements grow. Enterprise SSO, passkeys, suspicious-login detection and compliance questionnaires each add work that has to be maintained and patched for years. A provider gives you those features sooner in exchange for a recurring fee that usually grows with user numbers, some dependence on a third party, and a migration project if you ever leave. Ask any development team which parts they would write themselves, which they would take from the framework, and what happens to user accounts if you change provider.
Account recovery is the weak point
An attacker who cannot beat your login will try your "forgot password" or "lost my phone" flow instead. If a passkey-protected account can be reset through a single email link, the account is only as safe as that mailbox. Recovery deserves as much design attention as sign-in.
NIST's guidance is a useful reference. Its account recovery section describes options such as recovery codes saved by the user at enrollment, codes sent to an address the user registered earlier, and trusted recovery contacts, and it requires that recovery always triggers a notification to the account holder. In practice: let users register more than one sign-in method, issue recovery codes when MFA is switched on, notify on every reset, and give support staff a written procedure so they cannot be talked into handing over an account.
Common mistakes to avoid
- Forcing complex password rules, regular password changes or security questions. NIST's guidance rules out all three and says to check new passwords against a list of common and compromised ones instead.
- Making MFA mandatory for a low-risk consumer app on day one, or leaving it optional for administrators who can see everyone's data.
- Treating login as finished at launch. Rate limiting, session expiry and monitoring belong in the same plan; our web application security checklist covers those wider controls.
How to choose for a first release
Start from who your users are and what a stolen account would cost them. As an illustrative starting point, a consumer app can launch with email sign-up, Google and Apple login, optional passkeys and a carefully designed recovery flow. A B2B product can launch with email and password plus an authenticator app or passkey, MFA required for administrators, and a data model that is ready for SSO when the first larger customer asks. Apps that handle money, health or other sensitive records should require MFA for everyone and favor phishing-resistant methods.
Then write down three things before development starts: which sign-in methods are in the first release, how a locked-out user gets back in, and who is responsible for keeping the login system updated after launch. Regulated sectors may have their own authentication rules, so confirm those with a qualified adviser; nothing here is legal advice.
Conclusion
There is no single best login method. Passwords remain a baseline, social login reduces friction for consumers, SSO is what business buyers ask for, MFA limits the damage of a stolen password, and passkeys are now a standardized, widely supported way to remove the password from the picture. The strength of the whole system is set by its weakest path, which is usually account recovery.
If you are planning an app and want help deciding which login options belong in the first release and whether to build or buy them, you can request a quote and describe your users and requirements.