Identity Glossary

We've put together a glossary of identity terms for newcomers and seasoned developers, alike. Hopefully this helps put any identity terminology confusion to rest.


  • Access Token

    A credential that can be used by an application to access an API. It informs the API that the bearer of the token has been authorized to access the API and perform specific actions specified by the scope that has been granted. An Access Token can be in any format, but two popular options include opaque strings and JSON Web Tokens (JWT). They should be transmitted to the API as a Bearer credential in an HTTP Authorization header. See Access Tokens.

  • Audience

    The unique identifier of the audience for an issued token, identified within a JSON Web Token as the `aud` claim. The audience value is either the application (`Client ID`) for an ID Token or the API that is being called (`API Identifier`) for an Access Token. At Auth0, the Audience value sent in a request for an Access Token dictates whether that token is returned in an opaque or JWT format.


  • Callback

    The URL to which Auth0 sends its response after authentication. It is often the same URL to which a user is redirected after authentication.

  • Claim

    An attribute packaged in a security token which represents a claim that the provider of the token is making about an entity.

  • Confused Deputy

    The term confused deputy refers to a situation in which an attacker tricks a client or service into performing an action on their behalf.


  • Digital Identity

    The set of attributes that define a particular user in the context of a function which is delivered by a particular application.

  • Digital Signature

    A digital signature protects bits in a token from tampering. If the bits are changed or tampered with, the signature will no longer be able to be verified and it will be rejected.

  • Directory

    A centralized repository of users (the most well-known of which is Active Directory) which centralizes credentials and attributes and makes it unnecessary for each application to have their own local identity setup and pool of users. Allows single sign on to all applications that use the same directory of users.


  • ID Token

    An ID Token is a token meant for the client itself, rather than for accessing a resource. It has a fixed format that clients can parse and validate.


  • JSON Web Token (JWT)

    An open, industry standard RFC 7519 method for representing claims securely between two parties. At Auth0, ID Tokens are always returned in JWT format, and Access Tokens are often in JWT format. You may decode well-formed JWTs at to view their claims. See JSON Web Tokens.


  • Lock

    Auth0's UI widget for authenticating users. It is ready to go as-is and is the default face of the Classic Universal Login experience. Lock allows you to customize minor behavioral and appearance options, but its primary goal is ease of use. See Lock.


  • Multi-factor authentication (MFA)

    An authentication process that considers multiple factors. Typically at Auth0, the first factor is the standard username/password exchange, and the second is a code or link via email or SMS, a one-time-password via an app such as Authy or Google Authenticator, or a push notification via a phone app such as Guardian or Duo. Using multiple factors allows your account to remain secure if someone captures one or the other factor--acquires your password or steals your phone, for example. See Multi-factor Authentication.


  • Nonce

    An arbitrary (often random or pseudo-random) number issued in an authentication protocol that can be used to help detect and mitigate replay attacks using old communications. In other words, the nonce is only issued once, so if an attacker attempts to replay a transaction with a different nonce, its false transaction can be detected more easily. See Nonce.


  • OpenID

    An open standard for authentication that allows applications to verify users are who they say they are without needing to collect, store, and therefore become liable for a user’s login information. See OpenID Connect (OIDC).


  • Passwordless

    A form of authentication where the first factor is not a password. Instead, it could be a one-time password received by email or SMS, a push notification, or a biometric sensor. Passwordless uses one-time passwords, so users are less susceptible to the typical password-based attacks (e.g., dictionary or credential stuffing) than with traditional username/password logins. See Passwordless.

  • Perimeter

    A set of boundaries that encompass a directory, all of its users, and all of the applications which use the directory. In some implementations, this perimeter is a physical location; in others, it is a set of networks or devices connected via VPN.


  • Raw Credentials

    A shared secret or set of information that are agreed upon between the user and the resource that allow the resource to verify the identity of a user.

  • Refresh Token

    A special kind of token that can be used to obtain a renewed Access Token. It is useful for renewing expiring Access Tokens without forcing the user to log in again. Using the Refresh Token, you can request a new Access Token at any time until the Refresh Token is blacklisted. See Refresh Tokens.

  • Role

    An aspect of a user’s identity assigned to the user to indicate the level of access they should have to the system. Roles are essentially collections of permissions. See Role-based Access Control (RBAC).


  • Scope

    A mechanism that defines the specific actions applications can be allowed to do or information that they can request on a user’s behalf. Often, applications will want to make use of the information that has already been created in an online resource. To do so, the application must ask for authorization to access this information on a user’s behalf. When an app requests permission to access a resource through an authorization server, it uses the Scope parameter to specify what access it needs, and the authorization server uses the Scope parameter to respond with the access that was actually granted. See Scopes.

  • Security Assertion Markup Language (SAML)

    An XML-based standardized protocol by which two parties can exchange authentication information without the use of a password. See SAML.

  • Security Token

    A digitally signed artifact which is used to prove that the user was successfully authenticated

  • An entity emitted by a middleware after it establishes that the token it is receiving is signed, valid, and comes from a trusted source (the identity provider). This entity represents the fact that successful authentication occurred with the identity provider. This cookie prevents this process with tokens from needing to be continually repeated, by allowing the user to be considered authenticated as long as the cookie is present.

  • Shadow Accounts

    A difficult to sustain practice of manually provisioning a user from a local directory separately in a remote directory (essentially creating a copy, or shadow, of the original account) when they need access to remote applications.

  • Single Sign-On (SSO)

    A service that, after a user logs into one application, automatically logs that user in to other applications, regardless of the platform, technology, or domain the user is using. The user signs in only one time (hence the name of the feature). Similarly, Single Logout (SLO) occurs when, after a user logs out from one application, they are logged out of each application or service where they were logged in. SSO and SLO are possible through the use of sessions. See Single Sign-On and Single Logout.


  • Trust

    A resource trusts an identity provider or authority when that resource is willing to believe what the authority says about its users.


  • Universal Login

    Auth0’s implementation of the authentication flow, which is the key feature of an Authorization Server. Each time a user needs to prove their identity, your applications redirect to Universal Login, and Auth0 will do what’s needed to guarantee the user’s identity. See Auth0 Universal Login.