Access token

In computer systems, an access token contains the security credentials for a login session and identifies the user, the user's groups, the user's privileges, and, in some cases, a particular application.

An access token is an object encapsulating the security identity of a process or thread. A token is used to make security decisions and to store tamper-proof information about some system entity. While a token is generally used to represent only security information, it is capable of holding additional free-form data that can be attached while the token is being created. Tokens can be duplicated without special privilege, for example to create a new token with lower levels of access rights to restrict the access of a launched application. An access token is used by Windows when a process or thread tries to interact with objects that have security descriptors (securable objects). An access token is represented by the system object of type Token.

An access token is generated by the logon service when a user logs on to the system and the credentials provided by the user are authenticated against the authentication database. The authentication database contains credential information required to construct the initial token for the logon session, including its user id, primary group id, all other groups it is part of, and other information. The token is attached to the initial process created in the user session and inherited by subsequent processes created by the initial process. Whenever such a process opens a handle to any resource which has access control enabled, Windows reconciles the data in the target object's security descriptor with the contents of the current effective access token. The result of this access check evaluation is an indication of whether any access is allowed and, if so, what operations (read, write/modify, etc.) the calling application is allowed to perform.

There are two types of tokens available:

A token is composed of various fields, including:

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