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.


  • 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.


  • 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).


  • 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.

  • 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.

  • 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.


  • 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.