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Authentication is the process of validating that a user, device, or service is who or what it claims to be before granting access to an application or resource. It works by checking one or more factors: something you know, like a password; something you have, like a phone or security key; or something you are, like a fingerprint or face scan. For organizations, getting this right is about more than a login screen. The right authentication strategy shields sensitive data, stops account takeovers, and holds up smoothly at scale, even as credentials continue to flood the dark web.
This guide unpacks what authentication is, how it works, the main authentication types and protocols in use today, and how to choose the right approach for your application.
Main points
The cornerstone of digital security: Authentication serves as the first and most critical defense against cyber threats and data breaches, which means it’s constantly under attack.
Passwords on the way out: While traditional credentials remain common, businesses are rapidly adopting passwordless solutions for better security and user experience.
Implementation determines success: The right authentication approach balances strong security with a smooth user experience, requiring careful planning for your specific use case.
At a glance
Authentication is the process of verifying that a user, device, or service is who or what it claims to be before granting access to an application or resource.
It works by checking one or more factors: something you know such as a password, something you have such as a phone or security key, and something you are such as a fingerprint or face scan.
Common methods include password-based login, token-based authentication, certificate-based authentication, multi-factor authentication, passwordless authentication, adaptive authentication, and biometric authentication.
In 2026, the strongest patterns are passwordless and phishing-resistant login with passkeys, plus adaptive multi-factor authentication that steps up only when risk is high.
Choosing the right approach depends on your users, your risk profile, your compliance needs, and whether you also need to authenticate machines and AI agents, not only people.
Quick facts
What authentication is | The process of verifying that a user, device, or service is who or what it claims to be before granting access. |
Who needs it | Any application, system, or service that has to distinguish legitimate users from everyone else, from consumer apps to enterprise systems to machine-to-machine communication. |
How it differs from authorization | Authentication confirms identity (“who are you?”); authorization determines permissions (“what are you allowed to do?”). |
Core factors | Knowledge (something you know), possession (something you have), and inherence (something you are). |
Key outcome | Blocked account takeovers, reduced fraud, and access decisions that hold up under audit, without adding unnecessary friction for legitimate users. |
What is authentication?
Authentication is how digital systems ensure users (or devices and services) are who they claim to be, using everything from passwords to fingerprints. Think of it like staying at a hotel: a keycard proves a registered guest’s identity and unlocks their specific room. Both hotels and online services want only legitimate access, but keeping digital “keycards” safe presents a challenge.
A simpler everyday version of this happens dozens of times a day: unlocking your phone with a face scan, or opening your banking app with a fingerprint. In both cases, the device is authenticating you before it shows anything sensitive, and it’s doing it in under a second.
Case in point: the Verizon 2026 Data Breach Investigations Report highlighted credential abuse appeared at some point in 39% of all breaches. That’s why businesses are moving away from passwords toward more secure, user-friendly methods that keep cybercriminals out without making life harder for everyone else.
Authentication vs. authorization
Authentication and authorization answer two different questions. Authentication asks “Who is the user?” and confirms identity, a bit like checking a guest’s ID at a hotel. Authorization asks “What are they allowed to do?” and determines permissions, if a keycard lets them onto the lounge level, for example.
What it checks | When it happens | Example | |
|---|---|---|---|
Authentication | Identity: is this really the claimed user? | At login, and again at step-up moments | Entering a password or scanning a fingerprint to sign in |
Authorization | Permissions: what can this identity access? | After authentication, on every protected action | A plan member can update their device but not cancel the account |
Here’s how they work in practice: when a customer logs in to their mobile carrier account, authentication confirms their identity. Once in, authorization controls what they can access. Maybe they’re a member of the plan, but not the account manager. They can make changes that affect their phone number and device, but can’t order a service upgrade or cancel the subscription.
User authentication vs. machine authentication
Authentication isn’t just for humans. Machines (i.e., devices, apps, etc.) need to prove who they are, too, and increasingly so do AI agents acting on a person’s behalf. Understanding all three, alongside the user authentication methods each relies on, gives a fuller picture of authentication security.
User authentication is what most people think of when anything related to auth comes up. It’s the process where humans prove who they are to access systems, apps, and data. User authentication ranges from typing in a password, scanning their face or fingerprint, or entering a one-time code. Ultimately, it focuses on confirming human identity and is designed around human capabilities and behaviors.
Machine authentication (also known as machine-to-machine or M2M authentication) is how devices, applications, and services confirm identities with each other. Think of it like a handshake between two systems. For example, a smart home thermometer reports temperature readings to a cloud server, which requires it to authenticate with the remote service.
The primary use cases for M2M authentication are API communication, microservices, IoT and smart devices, and cloud networking. While each of these scenarios might use a slightly different type of machine authentication, such as access keys, client credentials flow, or Proof Key for Code Exchange (PKCE), they all require a machine to perform a backend “handshake” with another machine at some point in the journey.
Unlike user authentication, machine authentication happens automatically in the background and typically uses more complex credentials since there’s no human experience to consider. It’s also much more frequent, but since machines can complete authentication nearly instantaneously, it doesn’t negatively impact the user.
Agentic identity adds a third category that doesn’t fit neatly into either bucket: an agent often needs to act with a human’s delegated authority one moment and with its own scoped, machine-level credentials the next. That distinction is becoming a real design problem for authentication systems, not just a theoretical one, as more products ship agent-facing features.
Learn more: What Is Non-Human Identity (NHI)?
The three authentication factors
Authentication is designed around three fundamental factors:
Factor | Description | Examples |
|---|---|---|
Knowledge (something you know) | Information only the legitimate user should know. The most common factor, and also the most vulnerable. | Passwords, PINs, security questions, passphrases |
Possession (something you have) | A physical item that holds a digital secret. Requires both physical access and the ability to breach the device to compromise. | Smartphones, security keys (e.g., YubiKeys), smart cards |
Inherence (something you are) | A biometric trait that’s difficult to fake but requires specialized hardware to validate. | Fingerprints, facial recognition, voice patterns, iris scans |
Knowledge (something you know) includes passwords, PINs, security questions, and passphrases. These are the most common but also the most vulnerable. They can be guessed through brute force attacks, stolen through credential phishing, or compromised in data breaches. The challenge with knowledge factors is that to be truly secure, they need to be difficult for humans to remember and use.
Possession (something you have) relies on physical authenticators that hold a digital secret. These include devices like smartphones (which have dedicated hardware for auth secrets), security keys (e.g., YubiKeys), and smart cards. Such devices are highly secure because an attacker would need both physical access to the device and the ability to breach it. However, possessions can be lost, stolen, or damaged, which can necessitate less-secure fallback methods.
Inherence (something you are) uses biometric characteristics like fingerprints, facial recognition, voice patterns, and iris scans. These immutable and universal traits are extremely difficult to fake, but they require specialized hardware to validate. Biometric authentication also presents its own unique set of challenges, such as user pushback due to misunderstandings about how their data is used.
How does authentication work?
Authentication is a fundamentally simple process. When a user tries to log in to a system, that system determines the validity of one or more authenticators used to claim a digital identity (such as a password). Only two results are possible: “access granted” or “access denied.”
But while the concept of authentication is quite simple, the process of authenticating a user has become significantly more complex over the years. Let’s break it down into its core components.
The basic authentication process
Every authentication system follows the same core fundamentals and standards, like those defined in NIST SP 800-63-4:
Identity claim: The claimant (the user) asserts an identity to the system (such as with an email or username)
Authenticator presentation: The claimant presents one or more authenticators as proof (password, biometric data, a signed cryptographic challenge, security token, etc.)
Authenticator validation: The verifier (the system) validates the presented authenticators against stored authentication data
Access decision and session establishment: If validation succeeds, the system grants access and establishes a session with appropriate permissions
Using the hotel check-in from earlier: the guest states their name (identity claim), presents an ID or confirmation email (authenticator presentation), the front desk checks it against the reservation (authenticator validation), then hands over a keycard or flags a problem (access decision).
How authentication works in a web application
The same four steps above look like this in a typical web app:
The user submits credentials (a password, a passkey, an OTP) through a login form.
The server verifies those credentials against what it has stored, whether that’s a hashed password or a public key from a prior passkey registration.
If verification succeeds, the server issues a session or a token, most commonly a JSON Web Token (JWT), representing that the user is authenticated.
That session or token travels with each subsequent request, typically in a cookie or an authorization header.
The server validates the token on every request rather than re-checking credentials each time.
Access is granted or refused based on whether the token is valid, unexpired, and tied to the resource being requested.
Where standards fit into this flow: OAuth 2.0/2.1 and OpenID Connect (OIDC) handle the case where a user authenticates with a third party (like “Sign in with Google”) rather than directly with your app, and sessions or JWTs are simply the mechanism most frameworks use to avoid asking for credentials on every single request.
Importance of authentication
Authentication is critical to securing users’ sensitive data, whether it’s stored on networks, applications or systems.
Strong authentication is necessary for:
Security: Authentication is the most critical layer in your defense against account takeovers. Without strong authentication, even the toughest backend firewalls become meaningless once an attacker gains legitimate-looking access.
User experience: Poor authentication creates friction that drives users away. Complex password requirements, frequent re-authentication, and confusing multi-factor flows all contribute to user frustration and abandonment. Modern methods like passwordless auth can actually improve user experience while enhancing security.
Regulatory compliance: Industries like healthcare (HIPAA), retail and finance (PCI DSS), and government (FedRAMP) have strict authentication requirements. Failing to implement proper authentication controls can result in hefty fines, regulatory body audits, and loss of certifications. Many regulations now specifically require multi-factor authentication for accessing certain data.
Modern authentication challenges and solutions
Today’s traditional, password-based authentication faces a crisis: credentials are routinely exposed, sold to the highest bidder, and even posted for free on underground networks. These billions of credentials are fed into botnets to attempt account takeovers en masse, prompting organizations to enforce increasingly demanding password policies.
Yet, users already struggle to create and remember complex passwords, which leads to password reuse (making them vulnerable to credential stuffing), thus, the cycle continues. This is why modern systems often implement multi-factor authentication (MFA), adopt passwordless methods, and layer in adaptive authentication.
A newer challenge is emerging alongside these: identity for AI agents and other non-human entities. Traditional authentication assumes a human is at the keyboard; agentic systems break that assumption by acting on a user’s behalf without a person present at every step, which means the identity model has to account for delegated, scoped, and revocable access rather than a single static login.
We’ll cover more about how these authentication strategies solve today’s challenges in the following section.
Types of authentication
Authentication can take many forms, and the right method depends on your organization’s security needs, user experience goals, and regulatory requirements. Below, we compare the most common types at a glance, then break each down in more detail.
Method | How it works | Security level | User experience | Best for |
|---|---|---|---|---|
Password-based | User enters a username and password, checked against stored values | Low | Familiar but frustrating; vulnerable to reuse and phishing | Legacy systems, low-risk applications |
Token-based | User presents a physical or software token tied to their account | Medium-high | Extra step, but not tied to memory | Financial transactions, sensitive data access |
Certificate-based | Digital certificate issued by a trusted authority verifies identity | High | Invisible to the end user once configured | Enterprise environments, machine identity |
Multi-factor (MFA) | Combines two or more factors from different categories | High | Adds a step, but only occasionally | Any account handling sensitive data |
Passwordless | Uses possession or inherence factors instead of a password | High | Faster and simpler than passwords | Consumer and enterprise apps alike |
Adaptive | Scores login risk in real time and adjusts required verification | High | Nearly invisible for legitimate users | Apps with variable risk across sessions |
Biometric | Verifies a physical trait like a fingerprint or face scan | High | Fast, requires compatible hardware | Mobile-first and device-bound experiences |
Password-based authentication
Password-based authentication is a method of verifying a user’s identity by requiring them to enter the password associated with their account.
To authenticate with the system, the user enters their username and password, which are then compared to the stored values in the system’s database. If the username and password match, the user is granted access.
Although this is the most common type of authentication due to its simplicity and convenience, it is also probably the least secure. Its core weakness is straightforward: passwords can be phished, reused across services, or guessed, especially if the password is weak or reused across multiple systems.
Token-based authentication
Token-based authentication is a method of verifying a user’s identity by requiring them to present a token that is associated with their account. The token is a physical device or a digital file that contains a unique identifier, such as a smart card, USB key, or a software token.
Token-based authentication provides an extra layer of security compared to password-based authentication, as the physical token is harder to steal or replicate than a password. They are often used in situations where strong authentication is necessary, such as accessing sensitive data or performing financial transactions.
However, although tokens are a reliable method of authentication, they are more expensive and less convenient. They can be lost, stolen, or damaged, so users must take appropriate measures to safeguard them.
Certificate-based authentication
This method verifies the user’s or machine’s identity by using digital certificates. A digital certificate is an electronic document typically issued by a trusted third-party authority. They contain the user’s digital identity, a public key, and the digital signature of the certification authority.
As digital certificates are difficult to forge or steal, certificate-based authentication is considered to be highly secure. Usually, it’s used in enterprise environments dealing with sensitive data. However, it is more complex to set up and manage than other authentication methods, so it’s not the most convenient method for widespread use.
Multi-factor authentication (MFA)
Multi-factor authentication, or MFA, requires users to verify their identities using two or more independent factors from different categories (which may or may not include a password) at the time of login. Two-factor authentication (2FA) is the most common version of MFA, with only two identification factors needed.
With rapidly growing application security risks, more businesses are starting to rely on MFA to secure their applications against cybersecurity threats.
Passwordless authentication
Passwordless authentication refers to a range of authentication methods used to verify a user’s identity without the need for passwords. Instead, passwordless authentication uses a combination of possession and inherence factors, such as:
Magic links – A URL sent via text message or email containing a token that allows the user to log in without requiring a password when they click on it.
One-time passwords (OTP) – Unique, dynamically generated codes with numbers and/or letters that grant one-time access to the user.
Authenticator apps – An authenticator app is a software application installed on the user’s device that generates time-based one-time passwords (TOTP).
Biometrics – A physical trait unique to the user, such as fingerprints, voice, face, etc.
Passkeys – A FIDO2-based credential tied to a device and, increasingly, the clearest line between modern and legacy authentication, since they’re phishing-resistant by design and sync across a user’s devices.
By removing passwords, passwordless authentication reduces the risk of unauthorized access, making it superior to other methods. Additionally, it’s more convenient for users, as they no longer need to remember complex passwords.
Passwordless authentication is used in a variety of applications, including online banking, ecommerce, and enterprise environments. As technology continues to advance, passwordless authentication is likely to become more widespread as a secure and convenient alternative to traditional passwords.
Adaptive authentication
Adaptive authentication scores each login attempt based on contextual risk factors: where the user appears to be located, whether they’re using a new device, etc. This scoring system determines next steps, such as whether they’ll be prompted to complete additional authentication (like MFA).
Also known as risk-based authentication (RBA), adaptive authentication balances security rigor with a smooth user experience. It lets legitimate users sail through with only necessary friction, while potential threats are caught as early as possible.
Biometric authentication
Biometric authentication verifies identity using a physical or behavioral trait: a fingerprint, a face scan, a voice pattern, or an iris scan. It’s the most common real-world expression of the inherence factor, and it’s become the default unlock method on most modern phones.
Biometric data is typically captured and matched locally on the user’s device rather than transmitted to a server, which limits what an attacker can steal even if they compromise the backend. The tradeoffs are hardware dependency (not every device has a camera or fingerprint sensor capable of secure capture) and user comfort. Some users are wary of biometrics due to misunderstandings about how the underlying data is stored and used, so clear communication about local-only processing matters for adoption.
Modern authentication protocols
Today’s authentication systems rely on standardized protocols that ensure secure, interoperable identity and access management across diverse platforms and services:
OAuth 2.0/2.1 is the industry standard for authorization, not authentication on its own. Notably, OAuth isn’t an authentication protocol on its own, but it is a core part of OpenID Connect (below). OAuth powers social login, like “Sign in with Google/Apple/Microsoft,” and it’s a key ingredient in modern AI security.
OpenID Connect (OIDC) adds an authentication layer on top of OAuth 2.0, and it’s the piece that actually confirms who the user is. OIDC is what actually authenticates users in modern single sign-on (SSO) systems.
SAML 2.0 (Security Assertion Markup Language) is an older SSO protocol still widely used in enterprise environments to exchange authentication data between an identity provider and an application. SAML works by securely exchanging authentication data between identity providers and applications.
WebAuthn and FIDO2 are the standards that make passwordless authentication possible in the browser, using public-key cryptography instead of a shared secret. They’re supported natively by modern browsers and operating systems.
System for Cross-Domain Identity Management (SCIM) automates user provisioning and deprovisioning (enabling and disabling access) across multiple systems, which is what keeps enterprise directories in sync as employees or customers join and leave.
These authentication protocols work together to create an interwoven, interoperable authentication ecosystem. Combined, they can create smooth auth experiences for users. For example, you might use OIDC to sign into an app with your Google account, while WebAuthn/FIDO handles the actual authentication through your fingerprint via passkeys.
Authentication best practices
Authentication best practices evolve over time, but industry standards (like those provided by NIST) and implementation successes serve as reliable barometers. The following tips and tactics will help you build authentication that is both secure and user-friendly.
Embrace passwordless authentication
Passwordless authentication reduces the risk of account takeovers and identity theft while improving user experience. 90% of users are aware of passkeys and 75% of users have enabled passkeys on at least one account, making passwordless a practical choice for modern applications. When launching a new auth method like magic links, email-based OTPs, or passkeys, consider gradually rolling out to a smaller cluster of users first.
Implement adaptive MFA
Not every login attempt carries the same risk. Adaptive MFA adjusts the level of validation required based on factors like device reputation, geolocation, and login behavior. This approach introduces unnecessary friction for legitimate, trusted users while strengthening security for suspicious activity. Consider requiring additional authentication steps only for high-risk scenarios like new devices or unusual locations.
Use phishing-resistant methods
Traditional MFA can still be vulnerable to phishing attacks and MFA bypass techniques. Prioritize phishing-resistant methods and factors that can’t be easily stolen or replicated, such as FIDO2-based passkeys built on device-bound biometrics. Avoid SMS-based codes when possible, as they’re susceptible to SIM swapping, man-in-the-middle (MITM), and adversary-in-the-middle (AITM) attacks.
Follow security fundamentals
Keep token expiration short, and use refresh tokens behind secure storage. Log activity in enough detail to catch anomalies, like a token being used from multiple locations at once. Enforce strict rate limiting to prevent bot-based attacks, and apply strong password policies if you decide to use traditional credentials. For example, you can integrate your password requirements with Have I Been Pwned to prevent users from setting their password to one that’s been breached previously.
Authentication in action: Real-world case studies
Planning and theorizing about authentication can certainly help you prepare for production, but eventually, it’s time to solve real business challenges. Authentication can have a huge impact on security, user experience, and the bottom line across a wide range of industries. Here’s how different sectors implement authentication to meet their specific needs:
Banking and finance
Pattern: risk-based branching for bot defense. GradRight, an EdFinTech platform helping students finance education abroad, required defense from bot attacks without affecting their user experience. They added conditional checks for bot traffic, automatically branching journeys based on the risk level. If the system uncovered a likely bot, it was given additional auth steps. Legitimate users continued undisrupted.
Ecommerce
Pattern: per-application session policy. CARS24, a multinational online car marketplace, serves diverse stakeholders, including customers, dealers, and internal users across multiple applications. CARS24’s authentication solution could set different session times, activity timeouts, and other settings to cater to each app’s security requirements, meeting the different needs of their diverse user base.
Insurance
Pattern: passkey-first with a documented fallback. Branch Insurance, a cloud-native insurance provider, moved to phishing-resistant passkey authentication to serve their 12,000+ independent insurance agents. They saw auth-related support ticket volume drop by about half, and saw 25% adoption in the first 90 days. They also created a fallback flow for the small fraction of devices that might not support passkeys, ensuring users never encountered unnecessary roadblocks.
Healthcare
Pattern: consolidated, compliant backend across portals. SmithRx, a full-service Pharmacy Benefit Manager, needed to unify authentication across multiple portals while implementing fine-grained access control for their complex healthcare ecosystem. By consolidating their authentication backend, they were able to significantly reduce development overhead while maintaining a HIPAA-compliant login experience.
SaaS applications
Pattern: SSO, SCIM, and tenant-level RBAC in one stack. Notch, an AI-native customer support platform, needed flexible authentication to serve both startups and enterprises. With their auth implementation, Notch customers gained the benefits of SSO, SCIM provisioning, and tenant-level access controls with RBAC.
How to choose the right authentication method for your app
The right method depends on what you’re actually optimizing for. Use this decision matrix to narrow the field:
If your priority is… | Consider | Why |
|---|---|---|
Strong security with low friction | Passwordless with passkeys | Phishing-resistant by design, faster than passwords, no shared secret to steal |
Uneven risk across sessions | Adaptive MFA | Applies extra verification only when risk signals warrant it, rather than every time |
Regulated industries with audit requirements | Phishing-resistant MFA with audit trails | Meets compliance mandates while producing the logging regulators expect |
Developer speed and no-code workflows | A platform approach | Visual workflow tooling ships auth changes without a full engineering cycle per update |
Identity for AI agents and non-human entities | A platform with native agent authentication | Traditional auth wasn’t built for delegated, scoped, machine-executed access |
For teams that need to authenticate both human users and AI agents, and want to do it through visual, no-code and low-code workflows rather than custom infrastructure, a platform purpose-built for both is worth evaluating rather than assembling the pieces separately.
Easy and secure authentication for your app
Authentication is at the heart of securing modern applications, and getting it right is critical for protecting your users, your data, and your business. From passwordless logins to adaptive MFA, the challenge is building strong, scalable flows without slowing development or adding friction.
Descope’s drag-and-drop CIAM platform helps organizations deliver secure, smooth authentication across every touchpoint, whether you’re securing customers, employees, partners, or AI agents, without the complexity of building it from scratch.
Get started with a Free Forever Descope account, or book a demo to see how we can support your authentication strategy.
