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Continuous authentication is the ongoing evaluation of an active session for signs that fraud or a change in trust conditions may have occurred. NIST SP 800-63B-4 calls this session monitoring, sometimes called continuous authentication. Instead of trusting a user indefinitely after sign-in, a service can reassess behavior, device and browser details, network and location information, and explicit identity or device events. Depending on policy, it may keep access active, request authentication again, end the session, or notify support.
It is not one product, sensor, or universal algorithm. Each organization chooses which signals to collect, how to weigh them, how quickly to react, and what recovery path legitimate users receive.
What continuous authentication means
NIST’s current terminology is precise: “Session monitoring (sometimes called continuous authentication) is the ongoing evaluation of session characteristics to detect possible fraud during a session.” The definition appears in NIST SP 800-63B-4, the final digital identity guideline published on July 31, 2025, which supersedes the previous SP 800-63B.
A normal sign-in evaluates credentials or an authenticator at one point in time. Continuous authentication adds checks after that point. A relying party, working with a credential service provider or identity provider and its verifier, can observe permitted characteristics of the session or receive security events from another system. It then compares the new information with an access policy and the expected state of the account, device, or session.
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The word continuous does not necessarily mean that a camera is constantly identifying a person. A system might use typing cadence, browser language, an abrupt change in network location, a device-compliance event, or an administrator’s token-revocation action. Some implementations assess a stream of characteristics; others primarily react to discrete events.
How the decision loop works
A practical model has four stages:
- Establish a session. The user signs in with the application’s accepted authenticator and receives a session or token.
- Observe or receive signals. During the session, the service monitors permitted characteristics, receives events from an identity provider, or uses both approaches.
- Evaluate policy. The application or resource service compares the new information with rules for the user, resource, device, location, assurance level, and current risk.
- Apply a response. The policy can allow the session to continue, require reauthentication or a step-up authenticator, revoke access, terminate the session, or notify a support or security team.
The signal itself does not dictate one response. A familiar browser-language change might be logged, while a disabled account or a revoked token might immediately block a sensitive resource. NIST places responsibility for acceptable risk and mitigations on the relying party.
Which identity signals can be used?
Signals are evidence about the session or the identity’s security state. They are not all equally reliable, stable, or privacy-friendly, so a design should document the purpose and limits of every signal.
Usage, velocity, and timing
A service can examine how an account is being used: request frequency, unusual velocity, timing patterns, or activity that differs from the session’s established baseline. For example, a sequence of actions that would be difficult for one person to perform in the observed time may trigger a step-up check. The sources do not establish a universal threshold or detection accuracy; those values are policy and implementation choices.
Behavioral characteristics
NIST lists behavioral biometrics such as typing cadence as an example. Keystroke rhythm can be treated as one contextual input while a session is active. It should not be presented as conclusive proof of identity: behavior can change because of stress, injury, a different keyboard, accessibility software, or another benign circumstance. A responsible policy therefore defines what happens when confidence falls and how the user can recover without being permanently locked out.
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Device and browser characteristics
Device and browser details can include the characteristics visible to the service, such as accepted languages. A change may indicate a new device, a modified browser, or a legitimate travel or software update. Device posture can also be supplied as an explicit event when a management system reports that a device is no longer compliant.
Geolocation and IP characteristics
Geolocation and IP-address characteristics provide network and location context. NIST gives the example of checking whether an address belongs to a block known for abuse. These signals can be imprecise: mobile networks, virtual private networks, corporate gateways, and shared addresses can make a user appear to move or share a location. A location result should therefore be tied to a documented policy and an appeal or reauthentication path rather than treated as an infallible identity test.
Identity-provider and credential events
Some of the most actionable signals are discrete events generated by the identity system. Microsoft Entra’s documented Continuous Access Evaluation (CAE) events include a user account being deleted or disabled, a password being changed or reset, multifactor authentication being enabled, an administrator revoking tokens, and elevated user risk being detected. CAEP event types include session revocation, credential change, assurance-level change, and device-compliance change. Supported events vary by implementation and integration.
Continuous authentication, continuous access evaluation, and CAEP
These terms are related but not interchangeable.
| Term | What it describes | What it does not guarantee |
|---|---|---|
| Continuous or session monitoring | Ongoing evaluation of characteristics of an already active session, such as behavior, device, browser, location, network, or identity status. | It is not a single product, algorithm, or requirement to use biometrics. |
| Continuous access evaluation | An implementation pattern in which an identity provider and resource service react to access-relevant changes while a token or session is still active. | It does not mean every system receives events instantly or supports the same event list. |
| Continuous Access Evaluation Profile (CAEP) | An OpenID Shared Signals profile that defines event messages exchanged by cooperating transmitters and receivers. | CAEP transports events; the receiving system still decides whether to continue, step up, or terminate access. |
The OpenID CAEP 1.0 specification defines event types for shared human or robotic users, devices, sessions, and applications. The OpenID Shared Signals specifications page lists CAEP 1.0 among the final specifications. Interoperability makes it possible for systems to exchange a common event format, but it does not impose one organization’s risk policy on another.
What happens when a signal changes?
Responses should be proportional to the resource and the confidence in the signal. Common actions include:
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- Continue access: Keep the session active when the information remains within policy.
- Step up authentication: Ask for a stronger or fresh authenticator before allowing a sensitive action. A FIDO2 security key can support this authentication step, but the key itself does not perform continuous monitoring.
- Reauthenticate: Require the user to sign in again when the session’s assurance is no longer sufficient.
- Revoke or terminate: End the session or reject subsequent resource requests when the account or token is no longer trusted.
- Notify support: Alert a security or help-desk process when investigation or human recovery is appropriate.
Event-based systems can act before an access token reaches its normal expiration. Microsoft describes CAE as enabling an application’s authorization to a resource to be revoked outside the lifetime of the access token. Checking token validity on every resource call can add a network round trip; event sharing can reduce that dependency, although it introduces its own propagation and integration requirements.
Microsoft Entra CAE as a concrete implementation
Microsoft’s Continuous Access Evaluation documentation describes a specific implementation rather than a universal behavior. In supported scenarios, the identity provider sends critical events to a resource service. The resource can reject a token that has not yet expired when a relevant condition changes.
Microsoft says critical-event evaluation aims to be near real time, but event propagation latency of up to 15 minutes may be observed. Its documentation identifies IP-location policy enforcement as instant. These timing statements apply to the documented Microsoft Entra implementation, supported services, and event types; they should not be generalized to other identity systems or to every event.
The implementation model and its rationale are described further in Microsoft’s guidance on securing applications with CAE. When comparing products, verify which applications and resource services support the feature, which events are transmitted, how a resource validates the event, and what users see when access is interrupted.
Why organizations use continuous evaluation
Reducing the post-change access window
Sign-in checks alone can leave a session usable after a password reset, account disablement, device-compliance failure, or administrator revocation. Monitoring and event sharing can shorten the period in which that stale session remains valid.
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Avoiding an overreliance on very short token lifetimes
Making tokens expire extremely quickly can increase prompts, network traffic, and failure opportunities without eliminating the risk between checks. Event-based revocation offers another control, provided that propagation, resource enforcement, and recovery are designed correctly.
Applying stronger controls to higher-value actions
Continuous checks can be risk-sensitive. A low-risk read operation might continue, while exporting a large data set or changing an account’s security settings requires fresh authentication. This approach lets policy reflect the impact of the requested action rather than treating every operation identically.
Privacy, fairness, and operational limits
NIST explicitly warns that most session characteristics have privacy implications. The collection, storage of expected subscriber characteristics, and processing of session characteristics must be included in a privacy risk assessment. Behavioral patterns, location, device details, and network history can reveal sensitive information beyond the immediate authentication decision.
Before enabling a signal, document:
- What data is collected and the specific security purpose for each item.
- Which teams, services, and administrators can access raw signals or derived risk scores.
- How long the data and baselines are retained, since no universal retention period is established by the cited guidance.
- How benign changes, false alarms, accessibility needs, travel, shared devices, and network translation are handled.
- How a legitimate user proves control of the account and regains access after a block.
- Whether an alternative authentication path exists if a signal is unavailable or inappropriate.
- How users are informed about monitoring and how exceptions are reviewed.
Signals can be noisy or change for harmless reasons. The available guidance does not provide a general detection-rate, false-positive rate, or accuracy guarantee. Behavioral biometrics alone do not establish a trustworthy identity, and continuous monitoring cannot guarantee that every compromised session will be detected.
How to design a continuous-authentication policy
- Classify resources and actions. Identify which applications, records, and administrative operations require the strongest assurance.
- Map the trust state. List the account, authenticator, device, session, network, and identity-provider conditions that must remain valid.
- Select the minimum signals. Choose behavioral, device/browser, location/network, risk, or discrete event signals only when they serve a documented purpose.
- Define thresholds and responses. For each signal and resource, specify when to continue, log, step up, reauthenticate, revoke, terminate, or notify support.
- Set freshness expectations. Record event-delivery targets, policy-evaluation timing, token behavior, and what happens during an outage or delayed event.
- Build recovery before enforcement. Test help-desk verification, backup authenticators, accessible alternatives, and user messaging before turning on automatic blocking.
- Assess privacy and access controls. Limit collection, protect stored baselines, restrict administrative access, and document retention and deletion.
- Test legitimate edge cases. Exercise travel, mobile networks, browser upgrades, shared workstations, device replacement, password changes, account disablement, and administrator revocation.
- Review integrations. Confirm that each identity provider, application, resource service, and event receiver supports the same protocol and response behavior.
How to compare implementations
A feature label is less informative than the controls behind it. Use these axes when evaluating an identity platform or building an internal service:
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| Comparison axis | Questions to ask |
|---|---|
| Signals | Does it use behavior, device and browser details, network or location, identity-provider risk, discrete credential events, device compliance, or a combination? |
| Freshness and response | How are events delivered, how long can propagation take, and can a resource reject an otherwise unexpired token? |
| Standards and integrations | Does it support CAEP or other Shared Signals profiles, and are the identity providers, applications, and resource services in scope? |
| Policy actions | Can administrators continue access, require step-up authentication, terminate sessions, revoke tokens, and notify support with separate rules? |
| Recovery | What does a legitimate user do after a false alarm, and can support verify the user without weakening the policy? |
| Privacy controls | Are purpose limitation, minimization, retention, access restrictions, transparency, and privacy assessment documented? |
Standards and terminology to anchor an architecture
NIST SP 800-63B-4 is the current federal digital identity guidance for authentication and authenticator management. It covers authenticator assurance and reauthentication and places session monitoring in that wider identity framework. It does not prescribe one commercial product or one set of behavioral signals.
CAEP and the broader Shared Signals work address communication between cooperating systems. A transmitter can publish an access-relevant event, and a receiver can use that information in its own policy engine. Because the receiver remains responsible for the decision, adopting CAEP does not automatically produce a particular lockout or reauthentication behavior.
Common misconceptions
“Continuous” means a person is watched by a camera
Not necessarily. The documented examples include typing cadence, browser and device characteristics, IP and location context, and explicit account or device events. An implementation can use one category, several categories, or no behavioral biometrics at all.
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No. A policy may log a low-confidence change, request stronger authentication for a sensitive action, or terminate only when an account or credential event warrants it.
CAEP enforces the receiver’s decision
No. CAEP defines event messages and the exchange between systems. The receiving service applies its own risk tolerance, resource policy, and recovery rules.
Event sharing is always instantaneous
No. Microsoft documents up to 15 minutes of propagation latency for some critical events in its Entra implementation and describes IP-location policy enforcement as instant. Other systems and events may behave differently.
Continuous monitoring replaces strong authentication
No. It supplements sign-in, authenticator assurance, reauthentication, and authorization policy. A strong initial authenticator and a usable recovery process remain necessary.
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Bottom line
Continuous authentication is best understood as session monitoring: repeated evaluation of identity, device, behavior, network, location, and security-state signals while access is active. Its value is the ability to respond when trust changes instead of waiting for the next sign-in or token expiration. The quality of an implementation depends on signal choice, event freshness, resource enforcement, proportional responses, privacy safeguards, and a recovery path that works for legitimate users.
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