What is Authentication as a Service (AaaS)?

Authentication as a Service (AaaS), also called Auth-as-a-Service, is a cloud-based model for delivering authentication capabilities through a managed service, APIs or software development kits (SDKs). It allows organizations to verify users and secure access to applications without building and maintaining every authentication function internally.

Depending on the service, Authentication as a Service can support user login, multi-factor authentication (MFA), passkeys, passwordless authentication, risk-based authentication, account recovery and authentication orchestration.

Some providers manage the entire authentication process, including identity accounts and login sessions. Others provide specialized authentication capabilities that integrate with an organization's existing identity provider (IdP) and applications.

Although Authentication as a Service is an industry term rather than a single formally standardized architecture, its underlying capabilities are supported by established authentication and identity standards, including NIST SP 800-63, OpenID Connect and WebAuthn. [1][2][3][4]

Authentication as a Service at a glance

Why is Authentication as a Service important?

Authentication is a critical part of securing digital services. Organizations need to establish that users are who they claim to be while protecting accounts and sensitive transactions against unauthorized access.

As digital services expand across web, mobile, contact centers and in-person interactions, organizations need to provide secure and consistent authentication across multiple customer touchpoints. Authentication as a Service can support this omnichannel approach by connecting authentication methods and verification processes across different channels, rather than requiring separate implementations for each interaction.

A customer may use a passkey to sign in, require additional verification before transferring funds or need a secure way to recover access after losing an authentication method.

Building, maintaining and updating these authentication processes internally requires ongoing technical expertise, security testing and operational management.

Authentication as a Service provides a way to access authentication capabilities through dedicated services rather than implementing every component independently.

Common benefits include:

• Reduced implementation overhead: Applications can integrate authentication capabilities through APIs, SDKs or standardized protocols.
• Consistent authentication controls: Organizations can apply common authentication methods and policies across supported applications and channels.
• Access to multiple authentication methods: Services may support passkeys, MFA, OTP and other verification methods through a common integration.
• Adaptable security: Risk-based and step-up authentication can apply additional verification when an interaction presents greater risk.
• Ongoing maintenance: Providers can manage supported authentication infrastructure, protocol updates and service operations according to their responsibilities.

These benefits are not automatic. They depend on the provider's architecture, security controls, available functionality and integration with the organization's existing systems.

NIST's Digital Identity Guidelines establish requirements for authentication processes, authenticator management and assurance levels, providing a technical foundation for evaluating authentication services. [1][2]

How does Authentication as a Service work?

Authentication as a Service connects an application to an external micro-service responsible for performing some or all of the authentication process.

The exact implementation varies depending on whether the organization uses a managed identity platform or an authentication service integrated into its existing infrastructure.

A typical authentication process involves five stages.

1. A user initiates an authentication request

The process begins when someone attempts to access an application, sign in to an account or perform an action requiring additional verification.

For example, a banking customer may attempt to log in or initiate a high-value transaction.

The application determines that authentication is required and initiates a request through the integrated authentication service.

2. The service evaluates the authentication requirements

The authentication service determines which verification method or process should be used.

Depending on the implementation, the decision may consider the user's registered authenticators, application policy and contextual information such as device characteristics, location or transaction risk.

Some services apply predefined authentication methods, while others support risk-based policies and conditional authentication journeys.

NIST recognizes the use of contextual indicators to help determine whether additional authentication controls are appropriate. [2][5]

3. The user completes authentication

The service initiates the required authentication method.

This may involve:

• Signing in with a passkey.
• Entering a one-time password.
• Approving a supported push authentication request.
• Completing a biometric authentication process.
• Providing an additional authentication factor for a sensitive action.

Each method has different security properties and assurance considerations. [2][4]

4. The service communicates the result

After the authentication process, the service communicates the outcome to the application.

In a federated architecture, an identity provider may issue a signed assertion or token that allows the application to recognize the authenticated user.

For example, OpenID Connect defines a standardized identity layer that enables applications to receive and validate authentication information from an identity provider. [3]

In API-based authentication models, the service may instead return a verification result that the application uses when deciding whether to continue an interaction.

5. The application determines the next action

The application evaluates the authentication result and applies the appropriate access or transaction authorization decision.

For example, a successful authentication may allow the user to access their account, proceed with a transaction or complete a sensitive account change.

Authentication and authorization remain distinct. Successfully verifying a user does not automatically mean they are permitted to perform every requested action. [3][6]

What authentication methods can Authentication as a Service support?

Authentication as a Service platforms may provide multiple methods for verifying users, depending on their capabilities and implementation.

Not all services support every method, and not every method provides the same level of security.

For example, passkeys based on WebAuthn can provide phishing-resistant authentication, while NIST SP 800-63B-4 classifies out-of-band authentication over the public telephone network, including SMS, as restricted [2][4]

Organizations should select authentication methods according to the risks, users and assurance requirements of the interaction.

What is an example of Authentication as a Service?

A financial institution using a cloud-based authentication service provides a practical example of Authentication as a Service.

Consider a customer initiating a high-value bank transfer.

The customer may have already signed in using a passkey, but the bank requires additional verification before allowing a particularly sensitive transaction.

Rather than building a separate verification process directly into its application, the bank can use an external authentication service to evaluate the transaction context and initiate an appropriate step-up authentication journey.

The service may assess available contextual signals, select an additional verification method and communicate the result to the bank's application.

The application then determines whether the transaction can proceed, taking into account the authentication result and its existing fraud and authorization controls.

This is an example of how Authentication as a Service can support risk-based verification without necessarily replacing the bank's existing identity provider or account management infrastructure.

The same approach may support account recovery, changes to registered authentication methods or other sensitive customer interactions.

What is the difference between Authentication as a Service and Identity as a Service?

Authentication as a Service (AaaS) and Identity as a Service (IDaaS) are closely related, but they describe different scopes of functionality.

Authentication as a Service focuses on verifying users and providing authentication capabilities through an external service.

Identity as a Service generally describes a broader cloud-based identity management model that may include authentication, user directories, identity lifecycle management, provisioning and federated access.

The distinction is not absolute. An IDaaS platform may deliver Authentication as a Service, and some authentication providers also offer wider identity management capabilities.

The key difference is the scope of responsibility: authentication services can focus on verifying users, while broader identity platforms may manage the underlying identities and their lifecycle.

What is the difference between Authentication as a Service and an Identity Provider?

An identity provider (IdP) is a system that authenticates users and communicates identity or authentication information to applications.

Authentication as a Service describes a delivery model for authentication capabilities.

An Authentication as a Service provider may operate as an IdP, but it does not necessarily have to.

For example, an organization may already use an identity provider to manage accounts and primary login.

It can integrate an additional authentication service to support adaptive MFA, passkey enrollment or step-up verification for sensitive transactions without transferring responsibility for its identity directory.

Alternatively, a fully managed authentication service may act as the identity provider itself and provide authentication results through federation protocols.

NIST SP 800-63C describes federated authentication architectures in which identity providers communicate authentication assertions to relying parties. [7]

The distinction is important because outsourcing authentication functionality does not always require replacing the underlying identity infrastructure.

How does Authentication as a Service support risk-based authentication?

Risk-Based Authentication uses contextual information to determine how an authentication attempt should be handled.

Authentication as a Service can provide the infrastructure and decision-making capabilities needed to apply these requirements across applications and customer interactions.

For example, a service may evaluate:

• Device information and recognized devices.
• IP address characteristics and geographic context.
• Unusual authentication patterns.
• Transaction type or value.
• The authentication methods available to the user.
• Other contextual or risk indicators supplied by an application.

Based on the available information, the service may allow an existing authenticated session to continue, request additional verification or return a result for the application to evaluate.

This approach is commonly associated with adaptive or step-up authentication.

NIST SP 800-53 includes an adaptive authentication control (IA-10) that describes requiring supplemental verification under defined conditions, such as suspicious behavior or the number or types of records being accessed. [5]

Risk-based authentication does not replace the need for appropriate baseline authentication controls. Instead, it allows additional requirements to be applied where necessary.

What is the difference between Authentication as a Service and authentication orchestration?

Authentication as a Service (AaaS) and authentication orchestration are closely related concepts, but they describe different aspects of authentication.

Authentication as a Service is a cloud-based delivery model that provides authentication capabilities through managed services, APIs or SDKs. These capabilities may include passkeys, multi-factor authentication, one-time passwords and risk-based verification.

Authentication orchestration is the process of coordinating authentication methods, policies and verification steps within a user journey. It determines which authentication methods are used, when additional verification is required and how the authentication process adapts to different conditions.

The two approaches can work together. An Authentication as a Service platform may include orchestration capabilities, allowing organizations to coordinate multiple authentication methods, build conditional verification journeys and support omnichannel authentication across web, mobile, contact centers and in-person interactions through a common integration.

For example, a financial institution may use Authentication as a Service to provide passkeys, biometrics and OTP verification, while authentication orchestration determines which methods are required based on the customer's device, transaction risk or previous verification outcomes.

Authentication as a Service provides the authentication capabilities, while authentication orchestration determines how and when those capabilities are used.

Related authentication terms

Multi-factor Authentication (MFA): Authentication requiring evidence from more than one distinct authentication factor.

Passkeys: Cryptographic credentials that support phishing-resistant authentication without traditional passwords. Learn more about passkeys.

Risk-Based Authentication: An approach that evaluates contextual signals to determine how an authentication attempt should be handled. Learn more about Risk-Based Authentication.

SMS OTP: A one-time password delivered through SMS to a registered phone number. Learn more about SMS OTP.

Identity Provider (IdP): A system responsible for authenticating users and providing identity information or authentication assertions to applications.

Identity as a Service (IDaaS): A cloud-based delivery model for identity and access management capabilities.

Authentication Orchestration: The coordination of authentication methods, policies and verification steps across user journeys.

Omnichannel Authentication: An approach that enables organizations to provide and coordinate authentication across multiple customer touchpoints, such as web, mobile, contact centers and in-person interactions.

Step-up Authentication: Additional authentication requested when an interaction requires greater security assurance.

Passwordless Authentication: Authentication that does not require users to enter a traditional password.

Federated Authentication: An approach that allows an application to rely on authentication performed by a trusted identity provider.

Authentication API: An application programming interface used to initiate, manage or evaluate authentication processes.

Frequently asked questions