Introduction
Passwords have been the standard method of authentication for decades, but they come with significant challenges. Users often create weak passwords, reuse them across multiple services, or become victims of phishing attacks. Organizations spend considerable resources managing password resets, enforcing password policies, and securing credential databases.
Passkeys are emerging as a modern authentication solution that eliminates many of these problems. Built on FIDO2 and WebAuthn standards, passkeys provide a passwordless authentication experience that is both more secure and more user-friendly.
Major platforms, including Windows, Android, iOS, Google, Microsoft, and Apple, support passkeys, making them increasingly practical for modern web applications.
In this article, you'll learn how passkey authentication works, its benefits, how it differs from traditional authentication, and how to implement passkey authentication in ASP.NET Core applications.
What Are Passkeys?
A passkey is a passwordless authentication credential based on public-key cryptography.
Instead of storing passwords, passkeys use:
When a user authenticates:
The server sends a challenge.
The device signs the challenge using the private key.
The server verifies the signature using the public key.
Since the private key never leaves the device, attackers cannot steal it through database breaches or phishing attacks.
Why Passkeys Are More Secure Than Passwords
Traditional password-based authentication introduces several security risks:
Weak passwords
Credential stuffing
Phishing attacks
Password reuse
Database breaches
Passkeys eliminate many of these threats.
Protection Against Phishing
Passkeys are bound to specific domains.
Even if users visit a fake website, authentication will fail because the domain does not match the original registration.
No Shared Secrets
Passwords are shared secrets stored on both the client and server.
Passkeys use asymmetric cryptography, eliminating shared secrets entirely.
Reduced Attack Surface
Attackers cannot:
This significantly improves authentication security.
Understanding WebAuthn and FIDO2
Passkeys are built on two key standards.
WebAuthn
Web Authentication (WebAuthn) is a web standard that allows browsers to communicate with authentication devices.
Supported browsers include:
FIDO2
FIDO2 defines secure authentication mechanisms using public-key cryptography.
Together, WebAuthn and FIDO2 enable passwordless authentication across devices and platforms.
How Passkey Authentication Works
A passkey implementation consists of two primary workflows:
Registration
The user creates a passkey.
Process:
User registers.
Server generates a challenge.
Browser creates a key pair.
Public key is sent to the server.
Private key remains on the device.
Authentication
The user signs in.
Process:
User enters username or email.
Server generates a challenge.
Device signs challenge using private key.
Server verifies signature.
Authentication succeeds.
No password is required.
Setting Up an ASP.NET Core Project
Create a new ASP.NET Core Web API project.
dotnet new webapi -n PasskeyDemo
Navigate to the project:
cd PasskeyDemo
Add a FIDO2 library.
dotnet add package Fido2
This package simplifies WebAuthn and passkey implementation in ASP.NET Core applications.
Configure FIDO2 Services
Register FIDO2 services inside Program.cs.
builder.Services.AddSingleton(
new Fido2NetLib.Fido2(
new Fido2Configuration
{
ServerDomain = "localhost",
ServerName = "Passkey Demo",
Origins = new HashSet<string>
{
"https://localhost:5001"
}
}));
This configuration defines the application's WebAuthn settings.
Creating a Registration Challenge
When a user begins registration, the server generates a challenge.
Example:
var options =
fido.RequestNewCredential(
user,
new List<PublicKeyCredentialDescriptor>(),
authenticatorSelection,
AttestationConveyancePreference.None,
null);
The generated challenge is sent to the browser.
The browser uses it to create a new passkey.
Handling Registration Responses
After the browser creates the credential, the public key is returned to the server.
Example:
var success =
await fido.MakeNewCredentialAsync(
credentialResponse,
options,
callback);
The server stores:
Credential ID
Public Key
User information
These records will be used for future authentication requests.
Creating an Authentication Challenge
When a user attempts to sign in, the server generates another challenge.
Example:
var options =
fido.GetAssertionOptions(
allowedCredentials,
UserVerificationRequirement.Required);
The challenge is sent to the client device.
The private key signs the challenge securely.
Verifying Authentication
The signed assertion is returned to the server.
Verification example:
var result =
await fido.MakeAssertionAsync(
assertionResponse,
options,
storedPublicKey,
storedSignatureCounter,
callback);
If validation succeeds, the user is authenticated.
The application can then create an ASP.NET Core authentication session or issue a JWT token.
Combining Passkeys with ASP.NET Core Identity
Many applications already use ASP.NET Core Identity.
Passkeys can be added alongside existing authentication methods.
Example workflow:
User registers with email.
User creates a passkey.
Passkey becomes the preferred login method.
Password acts as a fallback option.
This approach simplifies migration to passwordless authentication.
Issuing JWT Tokens After Authentication
API-based applications often use JWT authentication.
After successful passkey verification:
var token =
GenerateJwtToken(user);
The token is returned to the client.
return Ok(new
{
AccessToken = token
});
This allows secure integration with mobile apps, SPAs, and APIs.
Practical Use Cases
Passkey authentication is particularly valuable for:
Banking Applications
Protect sensitive financial accounts.
Enterprise Portals
Reduce password management overhead.
Healthcare Platforms
Secure patient and provider access.
E-Commerce Systems
Improve account security while simplifying login.
SaaS Platforms
Enhance user experience and reduce support tickets related to password resets.
Benefits of Passkeys
Organizations adopting passkeys gain several advantages.
Improved Security
Public-key cryptography provides stronger protection than passwords.
Better User Experience
Users can authenticate using:
Fingerprint
Face recognition
Device PIN
Security key
Lower Support Costs
Password reset requests decrease significantly.
Cross-Platform Compatibility
Passkeys work across:
Reduced Phishing Risk
Authentication only works on trusted domains.
Best Practices
When implementing passkeys in ASP.NET Core applications:
Use HTTPS in all environments.
Validate origins carefully.
Store credential metadata securely.
Enable multi-device passkey support.
Support account recovery mechanisms.
Combine passkeys with risk-based authentication where appropriate.
Monitor authentication logs.
Regularly update FIDO2 libraries.
These practices improve both security and reliability.
Common Challenges
Developers may encounter several challenges during implementation.
Device Compatibility
Older devices may not support passkeys.
User Education
Some users may be unfamiliar with passwordless authentication.
Recovery Workflows
Lost devices require secure account recovery procedures.
Migration Strategies
Organizations must decide how to transition from passwords to passkeys.
Planning for these scenarios ensures smoother adoption.
Conclusion
Passkeys represent a significant advancement in modern authentication. By leveraging WebAuthn and FIDO2 standards, organizations can eliminate many of the security risks associated with traditional passwords while delivering a faster and more convenient user experience.
ASP.NET Core provides an excellent foundation for implementing passkey authentication, whether through standalone solutions or integration with ASP.NET Core Identity. As passwordless authentication continues to gain adoption across major platforms and services, developers who understand passkeys will be well-positioned to build more secure and user-friendly applications.
For organizations seeking stronger security, reduced support costs, and protection against phishing attacks, passkeys offer a practical and future-ready authentication solution.